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@2007 Austin Troy
Lecture 4: An Introduction to the Vector Data Model and Map
Layout Techniques
Introduction to GIS
By Brian VoigtUniversity of Vermont
Thanks are due to Dr Troy and Dr Zhou, upon whose lecture much of this material is based.
@2007 Austin Troy
• Three basic “feature” or “object” types– Point
– Arc
– Polygon
• A layer holds a single feature type
Reviewing Vector Data Types
Introduction to GIS
@2007 Austin Troy
• Attribute table
• Attribute types– Nominal attributes: descriptive information– Ordinal attributes: rank order or scale– Interval/ratio attributes: numeric items, order,
magnitude of difference
Reviewing Vector Data Types
Introduction to GIS
@2007 Austin Troy
Point Feature• A point layer: a collection of records with (x,y) coordinates
Introduction to GIS
Image modified from ESRI Arc Info electronic help
0 1 2 3 4 5 60
1
2
3
4
5
6
2,2
6,3
5,5
3,6
1
2
3
4
ID X,Y Coordinat
es1 2,2
2 3,6
3 5,5
4 6,3
…
10 4,1
4,110
@2007 Austin Troy
Line (Arc) Feature• Feature has length but not area• Straight or curved• Lines connect a set of vertices and nodes• Feature is the ARC, not the line segments• Arcs meet at nodes
Introduction to GIS
Image modified from ESRI Arc Info electronic help
Line segment
Node
Vertices
Node
@2007 Austin Troy
Polygon Feature• Area of homogenous phenomena • In a polygon layer, lines (arcs) define areas• Closed region – first and last coordinate pairs are in the
same location• Line segments bound the polygon
Introduction to GIS
Lines (Arcs)
Points
@2007 Austin Troy
• Definition1: Explicit encoding of spatial relationships between objects: the spatial location of each point, line and polygon is defined in relation to each other
Introduction to GIS
Topology
• Definition2: Topology is a collection of rules and relationships that enables the geodatabase to more accurately model geometric relationships found in the world.
@2007 Austin Troy
• Two major purposes
Introduction to GIS
Why Topology
– Allows for powerful analysis tools
– Quality control mechanism
@2007 Austin Troy
• Arc-node topology
Introduction to GIS
Types of Vector Topology
• Polygon topology
• Route topology
• Region topology
@2007 Austin Troy
• Connectivity analysis
Introduction to GIS
Arc-node & Node Topology
Arc-node Topology Arc-node List
Image source: ESRI Arc Info electronic help
Direction
@2007 Austin Troy
Polygon-arc Topology
Introduction to GIS
Polygon-arc Topology
Polygon-arc List
The order does matter!
Image source: ESRI Arc Info electronic help
@2007 Austin Troy
• Adjacency
Introduction to GIS
Polygon-arc Topology
External polygon
Image source: ESRI Arc Info electronic help
@2007 Austin Troy
Introduction to GIS
Route Topology• Define paths based on series of arcs
Image source: ESRI Arc Info electronic help
@2007 Austin Troy
• Ensuring “logical consistency”– Define complex and nuanced rules governing
spatial relationships of features
• Data quality– Single layer quality control– Mutli-Layer quality control
Introduction to GIS
Quality control and topology
@2007 Austin Troy
• Say we have the following layers: parcels, sidewalks, right of way boundaries, building footprints, zoning
• Rules for spatial relationships– Lots must be enclosed polygons
– Buildings must be entirely within a lot
– Sidewalks must be outside a parcel polygon and entirely within the public right of way
– Lots must fall entirely within a single zoning class
– All lots must have access to a right of way
Introduction to GIS
Topology rules: Example
@2007 Austin Troy
Introduction to GIS
sliver polygon
does not share a border
• Single layer quality control
Quality control and topology
Dangles
undershoot
overshoot
@2007 Austin Troy
Introduction to GIS
• Multi-Layer quality control: Defining spatial rules between layers
Quality control and topology
– Polygon rules: e.g. Must Be Covered by Feature Class of
• ArcCatalog includes new tools for defining and validating topology rules (Book: Building a geodatabase)
– Line rules: e.g. Must not Self Intersect
– Point rules: e.g. Must be Properly Inside Polygons
@2007 Austin Troy
Spaghetti Data Model• Non-topological data model
Introduction to GIS
• Collections of line segments and points– Only stores features’ coordinates
– No real connection, topology or relationships
• Not for spatial analysis
• Generally come from CAD files or digitizing
• Can “clean” these data, using user-defined tolerances
@2007 Austin Troy
Introduction to GIS
Title
Legend
Neatline
North arrow
Scale bar
Notes
Data frame
Map Composition
@2007 Austin Troy
Layouts• Create a map for layout in ArcMap Layout view
View>>Layout view.
Introduction to GIS
@2007 Austin Troy
Introduction to GIS
Map Compilation• Geographic features
• Other map elements– Legend
– Title
– North arrow
– Scale bar
– Author
– Neatline
– Source of data
– Other objects…
@2007 Austin Troy
Layouts
Introduction to GIS
Give a title, e.g. land use
Symbol editing
• Legends are edited in the Legends property window: Accessed by double clicking the legends.
@2007 Austin Troy
ArcMap: data frame• More than one frame can be shown in layout view
Introduction to GIS
Frame 1
Frame 2
@2007 Austin Troy
Layouts: data frame• Create a new view or “data frame” in ArcMap
Introduction to GIS
@2007 Austin Troy
MXD Files
Introduction to GIS
• Mxd files are project files
– Save your layout
– All other preferences
– Data is not included
– With an extension .mxd
•File >> Save (As)
@2007 Austin Troy
Layer Files
Introduction to GIS
• Save symbology and setting
• Primarily for saving legend setting
• Opening a layer file will open the data layer with all the preferences saved
• With an extension .lyr
@2007 Austin Troy
Layer Files
Introduction to GIS
• Use layer files when you have lots of non-numeric categories
@2007 Austin Troy
Layer Package Files
Introduction to GIS
• Save symbology and settings AND the data!
• New at version 9.3.1
• With an extension .lpk
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