NetworkAnalysis

Tutorial

with

TNTmips®

NETWORK

ANALYSIS

page 2

Network Analysis

Before Getting StartedTNTmips® provides sophisticated network analysis tools that determine theoptimal path between two points with any number of stops and route controlparameters taken into consideration. A second mode of operation has you locatepoints, or centers, then identifies the linear components of the network thatshould feed that center (Allocate In) or that the center should service (AllocateOut). Again, the characteristics of the lines and nodes that comprise the networkare used in determining the result.

Prerequisite Skills This booklet assumes you have completed the exercises inthe Getting Started and Introduction to the Display Interface tutorial booklets.The exercises in those booklets provide basic knowledge on how to use the TNTproducts. Because network analysis is heavily dependent on attributes, youshould also complete the Managing Relational Databases and ManagingGeoattributes booklets, which focus on how databases are created and maintainedand how attributes are associated with elements in an object. This booklet doesnot present these basic skills again.

Sample Data The exercises presented in this booklet use sample data distributedwith the TNTgis software. If you do not have access to a TNTgis DVD, you candownload the data from MicroImages’ web site. The exercises in this booklet usethe objects in the NETWORK Project File in the NETWORK data collection.

More Documentation This booklet is intended only as an introduction to thefeatures in the Network Analysis process. The tutorial on Vector AnalysisOperations is also recommended if you are not familiar with vector structure andtopology.

TNTmips® Pro and TNTmips Free TNTmips (the Map and Image ProcessingSystem) comes in three versions: the professional version of TNTmips (TNTmipsPro), the low cost TNTmips Basic version, and the TNTmips Free version. Allversions run exactly the same code from the TNT products DVD and have nearlyall the same features. If you did not purchase the professional version (whichrequires a software license key) or TNTmips Basic, then TNTmips operates inTNTmips Free mode.

MicroImages’ web site is your source of the newest tutorial booklets on a widevariety of topics in geospatial science. You can download the tutorial booklets,an installation guide, sample data, and the latest version of TNTmips Free.

http://www.microimages.com

© MicroImages, Inc. 2000–2015

page 3

Network Analysis

Welcome to Network AnalysisThe Network Analysis process in TNTmips providestools for preparing and analyzing vector objects thatrepresent connected transportation networks. Theprocess provides two modes of analyzing of a prop-erly-prepared vector object: routing and allocation.The routing operation determines the optimal pathbetween the start point, intermediate stops, and endpoint you designate. In the allocation operation,you indicate the location of centers for influx ordistribution; the process then assigns each linearcomponent of the network to one of these centers formost efficient service.

Network Analysis relies on the attributes of nodesand lines to produce meaningful results. The pro-cess cannot produce a meaningful route withoutknowing about one-way streets and impassableintersections. Nor can the process make sensibleallocation decisions without knowing the capacityof the centers and the demand along the networklines. Many other attributes such as line length,speed limits, allowed turn directions, average timefor turns, stop lights and signs, average time of stop,and so on, allow you to more accurately describe theproperties of a road network. The closer the matchbetween the vector attributes and the real-worldsituation, the more accurate the optimal routing andallocation predictions will be.

Although the input geodata for this booklet isTNTmips Free-sized, once you begin saving data-base information such as turn impedance, the data-base tables are too large for TNTmips Free. If you arerunning Free, you can follow along and view inter-face components, but after page 10, you won’t actu-ally be able to do the steps.

Page 4 discusses theproperties of a vectorobject that is suitable forNetwork Analysis. Pages5–7 describe the Routinginterface and preferences.Default and attribute basedrouting solutions areexplored on pages 8–9along with starting a newroute on page 10. Theexercises on pages 11–15concern turn and directionalimpedance. Network nodeattributes features arediscussed on pages 16–18with the exercise on page19 moving on to networkline attributes. Page 20presents more informationon styles. The remainderof the booklet is devoted toallocation networks.

launch TNTmipsSTEPS

Vocabulary: A stop, orwaypoint, is an intermediatepoint along a route that mustbe visited. A center is apoint within a network towhich materials or people arebrought or from whichmaterials or services aredistributed.

page 4

Network Analysis

Prepare the Vector ObjectThe Network Analysis process operates on vector objects that represent connectedtransportation networks. In order for network analysis to produce accurate results,the vector object must faithfully represent the actual transportation network. Ifyou acquire or import the network data, be sure to examine the data to make surethat all lines are fully connected and that actual intersections are represented bylines connecting at vector nodes. You can use the Editor to close any gaps andmake the necessary connections.

Vector objects with network topology are ideally suited for use in the NetworkAnalysis process. Network topology rules allow a vector object to have nodeswherever the crossing lines actually intersect in the real world, while crossing linesthat don't represent a real-world intersection (such as a bridge or highwayoverpass) are not required to have a node at the crossing point. (Planar andpolygonal topology rules require a node wherever two lines meet or cross). When

you create or import a new network vectorobject, be sure to choose network topologyfor the new vector object to enable non-intersecting crossing lines.

If a transportation vector object has nodesat crossing points that do not representactual intersections (because line elementson either side of the node have differentattributes, for example), you can disableturns for those nodes when you set up thenode attributes (see page 11).

A local road crosseseastbound and westboundlanes of a limited-accesshighway and intersectsanother local road.

A vector object with networktopology has a node (yellowsquare) only at theintersection of the two localroads.

A vector object with planaror polygonal topologyrequires nodes where thelocal road crosses thehighway lanes.

Make sure that lines representingintersecting roads and streetsactually connect at vector nodes.Lines can be connected in the Editorif necessary.

page 5

Network Analysis

Network Analysis Routing Interface

STEPSchoose Geometric /Network Analysis

click on the Openicon or on [InputObject] and selectTGR31109 NETWORK youmade in the previousexercise* from theNETWORK Project File

Two or three windows open when you launch theNetwork Analysis process: Network Analysis, Net-work Analysis View, and Network Analysis LayerControls. (The latter window opens the first timeyou use the process and subsequently only if it wasopen when you last exited the process.) The Managerwindow provides access to drawing style and Data-Tip settings. The View window lets you choosedisplay operations and the active tool (zoom, recenter,select, and add stop or center). The majority of thefeatures directly related to network analysis areaccessed from the Network Analysis window.

A variety of features built into the Network Analy-sis process are available by clicking the right mousebutton. For example, a right click on a node or lineelement in the list of all such elements will pan thedisplay if the element is out of the current view.

opens Network NodeAttributes window

opens NetworkLine AttributeswindowAdd

Near Stop

Calculate RouteSave Route

Save Report

ClearRoute

Select Near Node

Add NearCenter

Select Near Line

Vocabulary: Impedance isthe opposition to flow along agiven line. Impedance canalso be thought of as thecost of travelling along agiven line. The path chosenby the routing process hasthe lowest total impedance.A barrier is a node thatcannot be crossed.

opensPreferences

window

DeleteSelectedStops

Open andSave StopsTables

You can get more displayarea in the same sizewindow using LegendView/ Show / None

* see bottom of page 4

Set DemandValue

change stoporder

add new stops

page 6

Network Analysis

PreferencesSTEPS

click on the Prefer-ences icon near thetop of the NetworkAnalysis window

click on [Basic Color] onthe General tab andselect pale yellow orleave the color as white,then click [OK]

check that the style sub-object under the vectorchosen in the last exerciseis selected (select it if not)

click on the Lines tab thenon one of the color buttonsand next on the Style/Active Line/Specify button;note the choices

click on the Nodestab and explore thechoices available

You can set the color of interface components andthe drawing style for network components in theNetwork Analysis Preferences window. The “Ba-sic Color” in the General panel refers to the back-ground color for all boxes that are not otherwiseassigned in the Network Analysis and NetworkLine and Node Attributes windows. All of thePreferences buttons that assign colors to interfacecomponents show the currently selected color. AllStyle choices apply to the drawing style for networkelements in the View window. “Standard” meanseither solid color or a symbol or line pattern se-lected from the Style Editor window, which openswhen you click on the Specify (pencil) icon. Other

This row applies to theAngle Impedance diagram.

These colors apply to the fields inthe Network Line Attributes window.

Note the node colorscorrespond to theirrespective fields.

This row applies tothe Network NodeAttributes window.

Note incomingand outgoingline colorscorrespond inthe turn matrixand graphic.

These styles are for the active nodeand any barriers in the View window.

choices are None (stylespecified in VectorLayer Controls is used)and By Script.

Style for active linein View window.

page 7

Network Analysis

Preferences for Routes and AllocationThe options in the Route and Allocation Prefer-ences panels relate almost exclusively to the draw-ing style in the View window. The Color button ineach panel changes not only the color for thecorresponding box in the Stops or Centers list, butthe color assigned to the active stop / center in theView window when the Style is set to Standard.Consult the tutorial booklet entitled Creating andUsing Styles if you are unfamiliar with designatingdrawing styles. The methods for assigning styles aredescribed in detail there.

You want to be sure you choose a distinctive style fordrawing routes. If the drawing style for the selectedvector uses attributes, you do not want to pick a routestyle that could cause the route to be confused withthe style assigned to a particular class of road. If youwant symbols or line patterns for allocation net-works, you want to choose ones that include the“variable” color. Use of the variable color allows acenter and its allocated lines to “match.” The colorused as variable for each symbol / pattern pair is thatassigned to the center when it is added.

STEPS

click on the Routetab then on the PathSpecify icon

click on the red tile in thecolor palette, enter 3Screen Pixels for the LineWidth, and click [OK]

click on the StopSpecify icon, set thepoint style to be a 6 pixelwide medium blue filledcircle, and click [OK]

click on the Allocate taband explore the choicesavailable

Adds label withordinal stopnumber.

Vocabulary: The ActiveStop and Active Center areselected by clicking on theirnode number in the Stops orCenters list, respectively—not by selection in the Viewwindow.

Adds points to indicateturn locations.

These buttons let you retaindrawing of the stops / centers

Route

Allocation

for the lastcalculated route/ allocation aftertheir deletionfrom the Stops /Centers list.

step 1 icon

step 3 icon

page 8

Network Analysis

STEPSposition the cursor overthe cloverleaf in the uppercenter of the Viewwindow (with focus) andpress the <+> key (plus)to zoom in

click on the AddNear Stop icon

click on the twointersections shown(nodes 118 and 124)

click on the CalculateRoute icon

note that the routeselected is not theshortest path

The purpose of this exercise is to demonstrate theimportance of assigning attributes to elements andusing those attributes for network analysis. Lineshave an impedance value of one (1.00) by default.Thus, unless you specify some other attribute(s) toprovide or contribute to impedance, the suggestedpath will incorporate the fewest number of lineswithout regard for distance or other factors.

In this exercise, the route calculated incorporates aline that is more than 2.5 times the length of twoother lines that provide a more direct path. How-ever, the result obtained is correct using the defaultsettings because the total impedance of the pathselected is less than for the shorter path. The totalimpedance in this case is equal to the number oflines, which is four for the path selected and five forthe shorter path.

A variety of node and line attributes may result inidentification of a path that seems intuitively wrong,such as this one. However, that’s why networkanalysis is so valuable; it uses the attributes youspecify and identifies the path with the least imped-ance. This path is often not the path you would pick

Default Routing Solutions

andhere

click here

Informationabout the routeis displayedhere after theroute iscalculated.

All added stopsare listed hereby nodenumber.

by eye.

page 9

Network Analysis

click on the ClearRoute icon and theNetwork Line icon,both in the NetworkAnalysis window

click on the EditQuery icon in theImpedance panel of theNetwork Line Attributeswindow

choose Insert / Field (ortype) to change the valuefor ImpedanceOfLine toLINESTATS.Length

remove any other state-ments from the query (orcomment them out byinserting a # at thebeginning of the line)

click on [OK] in the QueryEditor window

click on the ApplyQuery icon in theImpedance panel

click on the CalculateRoute icon

note the difference in theroute from that in theprevious exercise

Using Length to Assess CostSTEPSThe Network Line Attributes window opens when

you click on the Network Line icon in the NetworkAnalysis window. This window can be open at thesame time as the Network Node Attributes windowso you can work on the attributes for both elementtypes at the same time.

The Query Editor for linesprovides the three pos-sible means for assigningvalues to lines by query,which assign a default value of 1 to every line, so youcan see the syntax for each of the possibilities:assignment applies to the line as a whole(ImpedanceOfLine); applies in the start to end direc-tion (ImpedanceOfLineFromTo); or applies in theend to start direction (ImpedanceOfLine ToFrom).You need to remove or comment out the second twostatements if you are going to assign the same at-tribute to both directions of the line, otherwise theseparate directions will later be set to 1.0 and cancelany attribute assignment made to both directions.

The length of the routedecreases from 2.6 to 1.3 kmafter assigning length as theimpedance value.

Use these Editand ApplyQuery buttons.

Note the differencein impedancevalues once thequery is applied.

page 10

Network Analysis

STEPS

click on the ClearRoute icon in theNetwork Analysis window

click on the Selectionindicator for both of thenodes in the Stops Listor click on theInclude All icon

click on the DeleteSelected Stops iconbelow the Stops List

click on the AddNear Stop icon

click on the twointersections shown(nodes 183 and 157)

click on the CalculateRoute icon

Steps for a New Route

thenhere

clickhere

Choosing to clear a route removes the calculatedpath, but leaves all stops along the way. You canthen add more stops or adjust the order of the stops

and recalculate the route. To compute aroute that does not use some or all of thestops in the current route, the stops mustalso be deleted from the Stops List.

This exercise is intended to show you how to begina new route and to point out another type of problemyou will encounter unless you are using a vectorobject with network topology. Network topologyby itself is not sufficient to avoid these problemsunless nodes that represent intersections whereroads do not actually meet (for example, the over-pass / underpass situation) have been removed andthe appropriate lines joined. You will likely en-counter intersections where turns need to be dis-abled even with correct network representation ofthe roads. The most common instance is an inter-section where left turns are not allowed, but allvariants may be found including intersections whereright and left turns are permissible, but you cannotproceed straight across. The next exercise de-scribes how to accommodate all of these situations.

Impedance = path length

Impedance = number of lines

Although the path calculated when impedance isdetermined by line length appears to be a betterchoice, neither of the routes shown is legitimate.Both involve getting on the Interstate where there isno on ramp. Your result should be the same asshown at the left.

The path shown at the right also involves travelin the wrong direction on access roads. Themeans to prevent wrong-way travel is discussedin a later exercise.

page 11

Network Analysis

Disabling TurnsSTEPS

click on the SelectNear Node icon inthe Network AnalysisView window

click on the NetworkNode icon in the mainNetwork Analysis window

click on the node shown at7th and I-80 (node 184)

click on the first “7th” entryat the left of the turn matrixin the Network NodeAttributes window

right-click on each entry inthe matrix that representsa turn from I-80 onto 7th orvice versa

click on the node indicatedat Superior and I-80 (node156), and right-click on allentries that representturns between I-80 andSuperior

The turn matrix in the Network Node Attributeswindow appears as soon as you select a node usingthe Select Near Node tool or by clicking in the Nodebox in the Network Node Attributes window. Agraphic depiction of the intersection and all associ-ated lines is also shown. You can determine exactlywhich line is referenced in each row and column ofthe turn matrix by clickingon the row and columnheadings in the turn matrix.The line referenced thenappears in the correspond-ing color in the graphic.The rows represent the linesincoming to the selectednode while the columns rep-resent the lines outgoing from the node. The incom-ing / outgoing identification is repeated in the Data-Tip associated with each heading.

The turn matrix initially shows X’s for all U-turns(except at dead-ends). An X indicatesthat the turn is disabled. You disableother turns by right clicking in thecorresponding box. The initial im-pedance value is then replaced by anX. U-turns can be enabled by enter-ing a positive impedance value forthese turns.

7th andI-80

Superiorand I-80

If you can proceed in only onedirection from each incomingline, there should be only onenumeric entry in each columnof the turn matrix.

The turn matrix for node 184 shouldappear as above when complete.

The turn matrix for node 156 shouldappear as above when complete.

If you left-click in the turn matrix, a Prompt win-dow opens so you can alter any value. Negativeone (-1) is the numeric equivalent of disabled.

page 12

Network Analysis

Saving Assigned AttributesSTEPS

click on the ClearRoute icon

click on the CalculateRoute icon

note the significantalteration between thisroute and that determinedin the exercise on page 10

click on the WriteTable icon in the TurnImpedance panel of theNetwork Node Attributeswindow

click [OK] in the TurnTable window to acceptthe default table name anddescription

click on the Show LayerManager icon on thetoolbar in the NetworkAnalysis View window ifthe Layer Manager is notopen

select nodes for drawingby turning on the ShowNodes toggle in theVector Layer Controls

expand the vector layerand the nodes in theLayer Manager

turn on the Selecticon for nodes,and open the Turn table

click on the Selecticon on the NetworkAnalysis View windowtoolbar, and select indi-vidual nodes to view theassociated turn informa-tion (in particular nodes184 and 156, for whichyou disabled turns in theprevious exercise, butothers as well)

You have assigned attributes for both lines andnodes in the course of the exercises on the last fewpages. You will assign more attributes to lines inthe exercise on the next page, so we will wait to savethose attributes. Assigned attributes are saved asdatabase tables. These tables can be reloaded forsubsequent network analysis sessions. You canalso alter or add to the node and line attributeinformation and save it again, replacing the originaltable, or save it as an additional attributes table.You might want multiple attributes tables for thesame vector object depending on the focus of thenetwork analysis. For example, the ability to usecertain streets or cross certain intersections may bequite different depending on whether the calculatedpath is intended for vehicles or pedestrians.

In order to view database records associated withselected elements, those elements must be selectedfor drawing and the Select tool must be active.Attached records are not located when you use theSelect Near Node tool that identifies associated

Node 184

The Turn table includesentries only for fields in theturn matrix with non-zeroimpedance values. Thistabular view shows all theturn impedance informationassociated with node 184.

node informationin the Node At-tributes window.

page 13

Network Analysis

Marking One-Way StreetsSTEPS

zoom up on the cloverleaf

with the Network Linesicon on (NetworkAnalysis window)click on the Select NearLine icon in the View

click on each of the eightlines and turn off thewrong-way direction byclicking on the greenarrow; look at the linediagrams (below and inthe Network LineAttributes window) andnode colors to determinethe direction to disable

Identifying disabled turns in the exercise on page 11changed the calculated route sufficiently that wrongway travel was no longer an issue when the newroute was calculated in the exercise on page 12.However, to prevent wrong-way travel for all routes,you need to mark one way streets. It is not necessaryto set the turn impedances to prevent turning thewrong way when unidirectionality has been as-signed to a line.

There are a total of eight lines in the cloverleaf thatrequire one-way assignment. The allowed direc-tions of travel are indicated by the arrows in thecloverleaf enlargement at the right. Some of theseroads have no name shown in the Network LineAttributes window because the original TIGER filedoes not have this attribute for these unnamedaccess and interchange roads.

When you click on a line in the View window, theline list automatically scrolls so that line is visible,and highlights it in the active line color both in theView window and in the list. The line and the twoassociated nodes are also shown in the upper rightof the Line Attributes window. The nodes are colorcoded so the direction of travel is easy to determine.

The settings for accessroads (top row) and inter-changes (bottom) are shownbelow starting at the Northand moving anti-clockwise.

click on the Write Tableicon in the Table panel ofthe Network LineAttributes window andaccept the default tablename

Single recordview of lineattributes forline 155 aftersaving table.

page 14

Network Analysis

Angle Impedance AssistantJust as some line characteristics, such as length andspeed limit, can be used to determine impedance forall lines, turn angle can be used to assign impedanceat all intersections. Angle impedance is not simplya property of nodes; it depends on which line(s) youuse to approach and leave the node. Assigning ahigher impedance to left than right turns implies alonger time delay for left than right turns, which isgenerally true (at least in countries that drive on theright). These impedance values are only assignedto enabled turns; recall that all U-turns, exceptthose on dead-end roads, are disabled by default.

The angles you select and values you enter in theAngle Impedance window define the spread inter-vals and ranges. A spread applies an even gradationbetween the impedance values set for one selectedangle and the next. In this exercise, angles from-179 to -90 have values evenly spread between 5 and1, respectively. Angles from -90 to 0 have imped-ance values from 1 to 0.1; angles from 0 to 90 havevalues spread from 0.1 to 3, and so on. As successiveangles are selected for inclusion in the spread, theirdots in the Angle Diagram are connected by an arc(in the Spread Range color). If you do not see acolored arc on the Angle Diagram, you have not yetselected two angles. Angles are deselected once aspread is applied.

STEPS

have the NetworkNode icon on in theNetwork Analysis window

if you have exited theNetwork Analysis processsince completing the exer-cise on page 12, click onthe Read Table iconand select the tablesaved in that exercise

click on the Edit iconin the Turn Imped-ance panel of the NetworkNode Attributes window

click on the first field in theAngle column (-179) andnote the dot (also in theSelected Angle color) inthat position on the AngleDiagram

click in the Impedancefield and change the valuefor this angle to 5

scroll down to -90 or clickinside the circle near -90in the diagram and scrollas necessary, then clickon -90 in the angle column

change the Impedancevalue for this angle to 1

repeat steps 6 and 7 butsubstitute 0 for theAngle and 0.1 forthe Impedance

repeat steps 6 and7 except substitute90 for the Angleand 3 for theImpedance

repeat steps 6 and7 except sub-stitute 180 for the Angleand 5 for the Impedance

click on [Spread]

You must click in theAngle column for a valueto be represented by adot in the Angle Diagramand included in thespread.

page 15

Network Analysis

3) Spread range from -150to -120 then from 120 to140 altered after initialspread and other changes.

Spread, Apply, and SaveSTEPS

click on [Apply]

click on [Write] and acceptthe defaults

click on [Close]

click on the Select NearNode icon, select node184, and compare the turnmatrix to that beforeapplying impedance fromthe Angle Diagram (seepage 11)

You can enter specific angle impedance values thatyou do not want to include in a spread by clickingin the impedance column to change the valuewithout also clicking in the Angle column (1, belowright). Such entered values will, however, bereplaced if you apply a spread over a range thatincludes the angle. You can also select a narrowedrange for spreading and alter the initial result in aportion of the Angle Diagram (2 and 3).

The Angle Impedance window keeps its last set-

1) Impedance values forindividual angles have beenincreased from that assignedby the spread.

spreadrangegraphicindicator

2) New, limited spread rangedefined (-120 to -150).

tings throughout the current Network Analy-sis session regardless of whether you applyany changes before you close the window. Ifyou want to “clear” the Angle Diagram,select 180 and -179, set them both to zero, and clickon the Spread button.

The Angle table you save is basically a “lookuptable” for the Turn table. If the value you see in theturn matrix is found in the Angle table, it is not alsosaved in the Turn table. If the value in the turnmatrix has been changed from the value assigned bythe Angle Impedance Diagram, it is stored in theTurn table. The Turn table you would get if yousave following this exercise is exactly the same asyou saved on page 12; you have not changed anynumeric impedance values from those determinedby the Angle Diagram.

The independence of the Turn and Angle tablesmakes it possible to mix and match these tableswhen determining routes and allocation. Just besure to read and apply the desired Angle tablebefore you read the Turn table. The Angle table actsas a lookup table for the Turn table, which keeps theTurn table from becoming any larger than neces-sary. The Turn table contains only the exceptionsto the information supplied by the Angle Diagram.

page 16

Network Analysis

Panning to Selected ElementsThere are so many features available in the NetworkAnalysis process that some will initially appearhidden from the novice user because the featuresare assigned to the right mouse button. You wereintroduced to a short cut for disabling turns avail-able from the right mouse button (page 11). You areintroduced to a number of other right mouse buttonfeatures in this exercise.

The Network Node Attributes window is also tiedto the Network Line Attributes window if you right-click an incoming or outgoing line name in the turnmatrix. A left click on the line name in the turnmatrix shows that line in the assigned color in thegraphic panel of the Network Node Attributeswindow. A right-click scrolls the line list in theNetwork Line Attributes window as necessary toselect the corresponding line and highlights the linein the View window.

STEPS

zoom up on the cloverleaf

click on the NetworkNodes icon if the Net-work Node Attributeswindow is not open

scroll the Node list in thiswindow and use the leftmouse button to click on avariety of node entries inthe list; note the View doesnot change

right-click on an entry inthe list and note the Viewscrolls to center the newlyselected node

right click onnode number

The Add Near Stop and Add NearCenter tools also have right button

features. Once astop or center hasbeen added to thelist, right-clickingnear it in the Viewwindow with theAdd Near Stop/Center tool activewill make it the ac-tive stop or center.

If you have not alreadytaken a break, before thisexercise is a good time forone. Select the same objectand read the saved tablesbefore beginning again.

left-click in turn matrix shows line inassigned color; right-click selects linein line list

page 17

Network Analysis

Network Node Attributes WindowYou have used the Network Node and Line At-tributes windows in a number of exercises withouta detailed description of the interface components.The time has come for such a description. Thewindows are presented separately because theirfeatures are so numerous and not all are furtherdiscussed in other exercises.

The graphic panel shows all lines attached to the active node. The elements shown areupdated by selecting a new node in the node list, using the Select Near Node tool in theView window, or clicking on a peripheral node to “walk” along a line (see next exercise).

Selection buttons letyou select nodes forapplication of groupaction (set/removebarrier).

The DataTips for the lines in the turnmatrix tell whether the line is incomingor outgoing relative to the active node,the line number, and the name of theline if named.

The DataTips for nodes tell whetherthe node is on a line, at an inter-section or a deadend and providesnames for the streets involved.

Opens AngleImpedance window.

Updates turn matrixwith previously savedTurn table values.

Creates Turn table fromvalues in matrix (seepage 15).

Turn matrix (you can scroll tosee all the values or, preferably,enlarge the window).

Number of linesattached to node.

Barrier indicator(red if barrier).

Clicking on name fields (left button)shows field and corresponding line (ingraphic panel) in incoming / outgoingcolor. Right-clicking highlights line inView window and, if open, in theNetwork Line Attributes window.

The Append / Subtract Selection icons add orsubtract the nodes selected in the View window tothe nodes selected in the Network Node Attributeswindow. Thus, you can use any of the generallyavailable selection tools, including selection byquery, to determine what is selected in the list.

STEPS

with the Network NodeAttributes window open,move the cursor down thenodes list, pausing forDataTips on a number ofdifferent nodes

click on a node field andobserve the DataTips forsome incoming andoutgoing lines in the turnmatrix

click on incoming andoutgoing line name fieldsin the turn matrix andobserve the effects in thegraphic panel

Turns on allSelection buttons.

Turns off allSelection buttons.

Toggles state ofSelection buttons.

Set Barrier status for selected nodes.

Remove Barrier status.

Read Barrier table.

Creates Barrier tablefrom current settings.

page 18

Network Analysis

Stepping through the NetworkSTEPS

with the Network NodeAttributes window openand a node selected, clickon one of the peripheralnodes in the graphic area

note the effect in theNetwork Node Attributeswindow and the Viewwindow

repeat steps 1 and 2several times (you neednot follow along a singleroad as shown in theillustration)

Each time you click a peripheral node (a node to oneside or the other of the currently selected node) in thegraphic panel of the Network Node Attributes win-dow, you change the active node for network analy-sis. The information for the new active node is shownin the turn matrix and the corresponding node isdrawn in active node style in the View window.Remember you can right-click on the active nodefield to scroll the contents of the View window if youstep to a node currently out of the View. You can alsoright-click on a line of interest in the turn matrix toscroll the line list in the Network Line Attributeswindow to show its information.

There is some ambiguity in the application of thewords active and marked to elements in the Network

clickhere

clickhere

Analysis process. When you use theGeoToolbox or queries to mark (se-lect) elements in the View window,you end up with an active elementthat is part (or all) of the marked set.There is no direct correspondencebetween this marked set and beingselected for network analysis opera-tions until you click on the Append/ Subtract Selection icon. The activeelement from the marked set does nottranslate into the active element fornetwork analysis in any case; thisactive status is only conferred byclicking on an element with the Se-lect Near Node / Line tool active or byclicking on it in the node / line list inthe corresponding Network Attributeswindow. Additionally, the activenode can be changed by the methodsdescribed in this exercise.

clickhere

page 19

Network Analysis

Network Line Attributes Window

Lets you enter animpedance value for allselected lines.

Enter/apply aquery todetermineimpedancevalues.

Lets you enter ademand value forall selected lines.

Enter/apply aquery to deter-mine demandvalues.

Open a network line attributes tableto update the impedance, demand,and disabled directions for lines.

The attributes for network lines are stored in asingle table that includes impedance, demand, anddirectional restrictions for each line in the object.The attributes for network nodes are stored in sepa-rate tables: Turn, Angle, Barrier, Stop, and Center.The Turn table is a special table that you cannotdirectly edit. It contains as many records for eachnode as are necessary to fully define turn impedancefor that node, which can be up to the square of thenumber of connected lines. The Angle table has 360or fewer records. The Barrier table has one record foreach node with a single logical (yes / no) field.

Save the current impedance,demand, and directionality oflines as a database table.

The graphic panel shows theactive line with end nodescolor coded to definedirection. The line shown isupdated by selecting a new

Selection buttonslet you select linesfor application ofgroup action (setdemand /impedance,enable/disabledirections).

The Append / Subtract Selection icons add or subtract thelines selected in the View window to the lines selected inthe Network Line Attributes window. Thus, you can useany of the generally available selection tools, includingselection by query, to determine what is selected in thelist. For example, you could disable all residential streetsfor large truck traffic.

Turns on allSelection buttons.

Turns off allSelection buttons.

Toggles state ofSelection buttons.

Enable/disabletravel in bothdirections for allselected lines.

Enable/disabledirection toggles.

STEPS

with the Network Nodeand Network LineAttributes windows open,right-click on one of theline names in the turnmatrix (Node Attributes)

note the effect in theNetwork Line Attributesand View windows

use the Select Near linetool to select a differentline

repeat steps 1, 2, and 3several times

examine the availableDataTips

line in the line listor using the SelectNear Line tool inthe View window.

Enter/apply aquery to setallowabledirections.

page 20

Network Analysis

More About StylesFor most vector applications, you are better off to usestyles stored as a subobject of the vector rather thanas a main level object. A style subobject keeps thedrawing styles with the vector so they do not getseparated inadvertently when transferring files. Thestyles used in Network Analysis, however, are notspecific to the input vector object but rather to thetemporary, network vector object generated in theprocess. You will want to have the same symbols andpatterns available for use with a variety of inputobjects. You can select a subobject for use, as youdid on page 6, but it is often difficult to remember justwhich vector has the desired subobject.

The style object used in this exercise has two sym-bols selected from the style objects provided withthe TNT products and several derived from glyphsin TrueType fonts. How to acquire symbols fromthese sources and how to create your own are de-scribed in the Creating and Using Styles booklet.

If you choose a sym-bol or line patternfor the active nodeor line, respectively,they will appear inthe View window as

designatedbut not in thecorrespond-ing NetworkAt t r i bu t e swindow. TheNetwork At-tributes win-dows incor-porate the ac-tive color butnot symbolicrepresenta-tion.

STEPS

click on the Preferencesicon in the NetworkAnalysis window

click on the General tab (ifit’s not already selected),then on the [Styles] button,and select the NETWORK-STYLE object from theNETWORK Project File

click on the Route tab andset the Active Stop color tomagenta (100% red, 100%blue)

with the Active Stop optionbutton set to Standard,click on its Specifyicon

set the Point Style Typeto Symbol, check the boxnext to the Happy Facesymbol, and set theHeight to 6 mm

with the Stop optionbutton set to Standard,click on its Specifyicon, set the PointStyle Type to Symbol,and select NeutralFacefrom the symbol list

set the Pathcolor as asolid, red line,1 mm width

place 4 or 5stops, thencalculatethe route

click on thestops list inthe NetworkAnalysiswindow tochange theactive stopand noticethe effect

page 21

Network Analysis

Allocation NetworksVocabulary: The AllocateIn function identifies thenetwork lines that should beused to bring people ormaterials to each identifiedcenter. Getting children toschool is an “Allocate In”operation. The Allocate Outfunction identifies thenetwork lines that should beused to distribute from acenter. Determining pizzadelivery areas for a pizzeriawith multiple locations is an“Allocate Out” operation.

Allocation refers to the movement of materials intoor out of a number of centers all of which serve thesame purpose, such as elementary schools, firestations, or warehouses. The line and node at-tributes you identify for routing are also relevant forallocation. For example, you probably want toinclude length as a factor in the impedance so thatthe distance traveled, rather than the number oflines, is used when making allocation assignments.Allowable turn directions may also make a differ-ence in which center a street is assigned to.

Additional constraints are important in identifyingcenters, such as the maximum capacity and theimpedance limit. Demand values are necessarybefore capacity limits can be meaningful. Each linehas a default demand value of 1.00 so that in theabsence of actual demand information, the capacityof a center is reached when the number of lines inits network equals the limit set. Impedance limits,such as the maximum distance of travel to a center,can be reasonably set and applied with no moreinformation than the standard vector attributes.

STEPS

click on the Allocate tab

move and pause thecursor over the variousicons to familiarizeyourself with theirfunctions

turn off display of nodes

Delete selectedcenters.

Set Capacityvalue.

Set Impedance Limit value. Run Allocate In operation.

Run AllocateOut operation.

Save the current allocationinformation for centers asa database table.

Clear currentallocation network.

Save information shownin Allocation Reportpanel as a text file.

Allocation information islisted here for each centerin the order added.

Turns off allSelection buttonsin the centers list.

Turns on allSelection buttons.

Toggles state ofselection buttons.

Centers arelisted herewhen added.

Set ImpedanceDelay value.

Note that the Network Node and Line Attributes and Preferences windows can beopen at the same time. Close these windows by clicking on their icons again.

Save currentcenters list.

Load previouslysaved centers.

page 22

Network Analysis

Allocation without ConstraintsSTEPS

click on the Add NearCenter icon in theView window

add four widely spacedcenters as illustrated

click on the AllocateOut icon and notethe results

examine the report

click on the ClearAllocation icon

click on the AllocateIn icon

compare the results

If at any time you exit the Network Analysis processand start again for one of the exercises, it is assumedthat you open the same object used throughout thisbooklet and reload the NETLINES, ANGLE, and TURN

tables for any exercise after page 15. (See page 15if you do not recall how to reload both turn andangle values.)

Demand, capacity, and impedance limits have dra-matic effects on an allocation network, as you willsee in later exercises. Without such constraints, alllines in the selected object are assigned to onecenter or another (unless attributes prevent assign-ment). The lines assigned to centers will oftenchange between Allocate In and Allocate Out op-

Allocate Out Allocate In

Node and line attributes affecta center’s line assignments.

erations where different center networks meetwhen line and node attributes are taken intoaccount. Expert evaluation is still requiredto assess the feasibility of the network, asshown at the left where one line switchescenter assignment between Allocate In andOut operations; it makes no sense for a distalline in a network to be a highway offramp.

AllocateOut

page 23

Network Analysis

Impedance LimitsAllocation networks are subject to additional con-straints that do not apply in the routing situation.One of these constraints is an impedance limit,which is the maximum impedance allowed for anypath to a center. You may own a business thatdelivers products from a number of locations anddiscover that there is some great advantage (insur-ance, vehicle wear and tear, customer satisfaction,or other factors) to limiting the delivery area foreach to 5 kilometers. You may, for example, wantto plan the location of schools so that children haveto walk no further than 2.5 kilometers. You thenenter the maximum desired travel distance as theimpedance limit. This limit can be the same for allcenters or different for one or more centers.

When impedance limits are set, all lines may not beassigned to one of the centers. You can simplyaccept these gaps in coverage, you can considerrepositioning centers to achieve complete cover-age, or you may rethink the limit you set. Unfortu-nately, we know of no algorithm that can determinethe “optimal” placement of centers so that the entirearea is covered with the fewest number of centers.

You enter a single value forall selected centers in thisexercise. You can set theImpedance Limit Value forindividual centers by click-ing in the Limit column forthat center in the CentersList. You can also use theSet Impedance Limit Valueicon with fewer than all ofthe centers selected, and theentered value will be as-signed only to those se-lected.

STEPS

click on the ClearAllocation icon

click on the IncludeAll icon at the leftabove the list of centers

click on the SetImpedance LimitValue icon

enter 2500 and click [OK]

click on the AllocateIn icon and note theresults

An impedance limit of 2.5km does not provide fullcoverage of the area withthe existing centers (blacklines are not covered).

AllocateIn

page 24

Network Analysis

Locating CentersOne strategy for locating centers that have animpedance limit is to first position a few centers ator near the periphery of the vector object and run thedesired Allocation operation. Next, reposition thecenters to be nearer to the interior edge of theallocation areas determined, and run the allocationagain.

The example on this page again points out theimportance of a knowledgeable user to determinehow the centers should be positioned initially andthen how they should be repositioned to improve theallocation results. It may not always be possible tofind locations for the desired number of centers withan impdance limit imposed, which may be accept-able. For example, if the centers are schools andsome areas fall outside the impedance limit, busingcould be provided for those areas. Other possibili-ties are to change the impedance limit so that morelines are included for each center or to increase thenumber of centers.

centers positioned near edgecenters moved to inner edge of originally

allocated area and reallocated

STEPS

click on the IncludeAll icon then on theDelete SelectedCenters icon (the 4thicon from the left, not therightmost)

add five centers positionedapproximately as shown

click on the IncludeAll icon then on theSet Impedance LimitValue icon, enter2500, and click [OK]

click on the AllocateIn icon

click on DeleteSelected Centers

add five new centerspositioned near an inneredge of the first allocationareas (except as shown)

repeat steps 3 and 4

set the ImpedanceLimit for all centersback to -1.0

page 25

Network Analysis

Establishing DemandEstablishing demand from the types of data gener-ally available is often not a straight forward task.Population is one of the most common factors usedto establish demand. However, population data isusually point data and demand is a line associatedattribute. You can use the Transfer Attributes pro-cess to associatethe point popula-tion data with thelines you plan touse for networkanalysis. Oftenvector objects in-clude an outline,such as city,county, or state boundaries, that does not representlines that can be used for travel. You can avoidattaching population attributes to such lines usingselected key field attributes or a query to limit thelines eligible for attribute transfer.

The method described forattribute transfer to linesoften results in the attachment of multiple records tomany of the lines (for example, household popula-tion data transferred to city streets). A special querystatement (shown below) is necessary for all attachedrecords, rather than just the first attached record, tobe considered when determining demand.

STEPS

choose Geometric /Attributes / TransferAttributes

click on [Source] andselect the vector objectthat contains points withattributes you want touse to establish demand

click on Destination andselect the object you willuse in Network Analysis

set the destinationelement to Lines and theselect option menu to ByAttribute or By Script*

click on [Select] andchoose the attributes orenter the query at theleft, then click [OK]

set the distance highenough that all records willbe transferred, and clickon [Run]

launch the NetworkAnalysis process, selectthe vector to whichattributes were transferredand follow the procedureon page 9 to assignimpedance by length

click on the EditQuery icon forDemand, entering thequery at the left but substi-tuting the name of yourtable and field for CITY andPOPULATION, respectively

click on the ApplyQuery icon in theDemand panel

This exercise is intended forappropriate data of your own.If you do not have such datanow, remember this refer-ence for when you acquiresuch data.

* Choose By Attribute only if the lineshave a key field attribute that distinguishes lines appropriate forinclusion in the network from those that are not. The scriptsuggested is intended only for the situation where all but the outerbounding lines are appropriate for use as network lines.

(Internal.LeftPoly > 0) and(Internal.RightPoly > 0)

DemandOfLine =SetSum(CITY[*].POPULATION)

Pointsfor attributetransferdisplayed overrecipientnetwork lines.

page 26

Network Analysis

Introducing CapacityCapacity is the number that can be accommodatedby a center. It may be the number of students aschool can accommodate, the quantity of perish-able goods that can be delivered in a day, thenumber of seats in a theater, or the number ofparking spaces at a mall. The capacity of the centersin a network can be the same or different. In orderfor capacity to be meaningfully used, you need areasonable estimate of demand. The default de-mand is 1.0 for each line. Thus, without altereddemand values, the capacity is reached when thenumber of lines feeding the center equals the valueset.

An exclusive area is established as network linesare allocated to centers such that once all paths to /from a center are assigned, that center’s area cannotbe increased even if the center is under capacity.There are a variety of options available to you as thedecision maker when you run into such circum-stances: change the position of centers, alter thecapacity of centers, or override the assignment ofcertain lines by manually reallocating territories.

If you did the last exercise,continue with that object forthis exercise. You will needto add centers and adjustcapacity values to be in linewith the demand youassigned.

STEPS

if you don’t have your ownvector with demand valuesassigned, pick up whereyou left off on page 24

click on the IncludeAll icon in theCenters List panel

click on the SetCapacity Value icon

enter 250 and click [OK]

click on the AllocateIn icon (or AllocateOut if more appropriate foryour demand data)

choose a center withunassigned lines on allsides, click on its capacityfield, enter 500, and click[OK]

again click onAllocate In (or Out)

scroll through the reportand note how closely eachcenter comes to being atfull capacity

Checking the report lets you judge

whether the capacityof planned centers is

sufficient or, perhaps,too great.

page 27

Network Analysis

More Complex Analysis

ance delay value for another center isreached. The center to which you wantlines assigned first should have an imped-ance delay value of zero. Other centersmay have the same or different highervalues assigned to them.

Network analysis problems may often re-quire a combination of many or all of thecontrol components available. You mayhave a number of closely spaced centersfrom which to deliver products but one haseasy access to a major highway, one is in ashopping district with little parking, and soon. You may want to organize your deliveries suchthat all addresses within a mile of the shoppingdistrict center are delivered by bicycle from thatcenter, intermediate distance deliveries are madeby car from a different center, and thehighway-convenient center makes deliv-eries by truck to more distant locations.The impedance delay feature helps youspecify such requirements. To ensure thatlong distance deliveries are allocated tothe desired center, you might also have toassign impedance limits to the other cen-ters to keep their delivery areas within citylimits.

The complexities of network analysis are many.Some have been specifically mentioned, othersalluded to, and still others await your discovery.

One concept not yet introduced that probably needssome explanation in this booklet is impedancedelay. Impedance delay lets network lines bepreferentially assigned to a center until the imped-

Changing the order of stopsis a simple matter. The initialconvoluted path shown herewas simplified by selectingstop 5 (click on node numberin Stops list) and clicking onthe Move Stop to End icon,then running the processagain.

click on CalculateRoute (3)

click here (1)click here* (2)

* these icons are belowthe Stops list

Advanced Software for Geospatial AnalysisNETWORK

ANALYSIS

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Indexadding stops ........................... 8, 10allocate in and out definitions ...21allocation networks ....................21allocation preferences .................. 7angle impedance ..................14, 15assigning length as cost ............... 9attribute importance ..................... 8barrier definition .......................... 5capacity ......................................26center definition ........................... 3disabling turns ............................11establishing demand ..................25impedance ........................ 5, 23, 27locating centers ..........................24Network Analysis interface .......... 5Network Line Attributes ......... 6, 19Network Node attributes ........ 6, 17

new route ....................................10one-way streets ...........................13panning to selected elements .....16preferences .............................. 6, 20Query Editor default ..................... 9right mouse button ....................... 5route preferences .......................... 7saving assigned attributes ..........12spread range ................................15stepping through network ..........18stop definition .............................. 3styles ...........................................20TNTlite ..................................... 2, 3turn matrix ..................................11turn table ....................................12vector topology and networks ..... 4waypoint definition ...................... 3

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