Grid-based GIS Modeling

Nigel TroddNigel Trodd

Modified from Berry JK, 2004. GIS Modeling, presented Modified from Berry JK, 2004. GIS Modeling, presented at at Grid-based Map Analysis Techniques and Modeling Grid-based Map Analysis Techniques and Modeling

Workshop, ASPRS Conference.Workshop, ASPRS Conference.

Aim and Objectives

By the end of this lecture you should better understand the By the end of this lecture you should better understand the process of map analysis. You should be able to:process of map analysis. You should be able to:

Read, design and implement a cartographical modelRead, design and implement a cartographical model Identify a logicalIdentify a logical processing sequenceprocessing sequence Calibrate and add weightings to model criteriaCalibrate and add weightings to model criteria Simulate alternative scenarios and different perspectivesSimulate alternative scenarios and different perspectives

Campground Suitability Model (Demo)

…evaluate a GIS model for Campground Suitability with the following criteria—

Prefer gentle slopes Prefer near roads Prefer near water Prefer good views of water Prefer westerly aspect

…can’t be too close to water or too steep (legal constraints)

Communicating Model Logic (suitability)

Decision Support Systems Framework

User-interface

Model

DB

Transmission Line Routing Model

CriteriaCriteria – the transmission line route should… – the transmission line route should…

Avoid areas ofAvoid areas of high housing densityhigh housing density

Avoid areas that areAvoid areas that are far from roadsfar from roads

Avoid areasAvoid areas within or near sensitive areaswithin or near sensitive areas

Avoid areas of highAvoid areas of high visual exposure to housesvisual exposure to houses

HousesHouses

RoadsRoads

Sensitive AreasSensitive Areas

HousesHouses

ElevationElevation

GoalGoal – identify the– identify the best route for an electric best route for an electric transmission linetransmission line that considers various criteria that considers various criteria for minimizing adverse impacts.for minimizing adverse impacts.

Existing PowerlineExisting Powerline

Proposed Proposed SubstationSubstation

Routing Model Flowchart (Model Logic—components)

Model logic is captured in a flowchart where the Model logic is captured in a flowchart where the boxes represent boxes represent maps and lines identify processing stepsmaps and lines identify processing steps leading to a spatial solution leading to a spatial solution

High Housing High Housing DensityDensity

Far from RoadsFar from Roads

In or Near In or Near Sensitive AreasSensitive Areas

High Visual High Visual ExposureExposure

Avoid areas of…Avoid areas of…

Routing Model Flowchart (Model Logic—maps)

Step 1Step 1

Identify overall Identify overall Discrete PreferenceDiscrete Preference (1-9 rating)(1-9 rating)

Step 1Step 1

Step 2Step 2

Generate an Generate an Accumulated Accumulated PreferencePreference surface surface from the starting from the starting location to location to everywhereeverywhere

Step 2Step 2

Step 3Step 3

Identify the Most Identify the Most Preferred RoutePreferred Route from the end from the end locationlocation

Step 3Step 3

Model logic is captured in a flowchart where the Model logic is captured in a flowchart where the boxes represent boxes represent maps and lines identify processing stepsmaps and lines identify processing steps leading to a spatial solution leading to a spatial solution

Step 1 Discrete Preference (friction) Map

… … identifies the identifies the relative preference (friction) of locating relative preference (friction) of locating a transmission line through any cella transmission line through any cell of the project area of the project area considering multiple criteriaconsidering multiple criteria

AVOIDLeast

Preferred

MostATTRACT

…average of the four individual preference

maps for overall preference at each cell

EXCLUDE (0)

Step 2 Accumulated Preference Map

… … identifies the preference to construct the identifies the preference to construct the preferred transmission line preferred transmission line from a starting from a starting

location to everywherelocation to everywhere in a project area in a project area

Cumulative cost surfaceCumulative cost surface

Step 3 Most Preferred Route (least-cost path)

PreferredPreferredRouteRoute

Preferred Route

… … the the steepest downhill path over the steepest downhill path over the accumulated preference surfaceaccumulated preference surface identifies the identifies the

most preferred route — minimizes areas to avoidmost preferred route — minimizes areas to avoid

Siting Model Flowchart (Calibrating and Weighting)

Model logic is captured in a flowchart where the boxes represent Model logic is captured in a flowchart where the boxes represent maps and lines identify processing steps leading to a spatial solutionmaps and lines identify processing steps leading to a spatial solution

Avoid areas of…Avoid areas of…

High Housing High Housing DensityDensity

Far from RoadsFar from Roads

In or Near In or Near Sensitive AreasSensitive Areas

High Visual High Visual ExposureExposure

RankingsRankings WeightsWeights

……but what is high but what is high housing density and housing density and how important is it? how important is it? …etc?…etc?

Calibrating Map Layers (Relative Preferences)

Model calibration refers to establishing a consistent scale from 1 Model calibration refers to establishing a consistent scale from 1 (most preferred) to 9 (least preferred) for rating each map layer(most preferred) to 9 (least preferred) for rating each map layer

1 for 0 to 5 houses1 for 0 to 5 houses……group consensus is that group consensus is that low housing density is low housing density is most preferredmost preferred

The The Delphi ProcessDelphi Process is used to achieve is used to achieve consensus among consensus among group participants. group participants. It is a structured It is a structured method involving method involving iterative use of iterative use of anonymous anonymous questionnaires and questionnaires and controlled feedback controlled feedback with statistical with statistical aggregation of aggregation of group response.group response.

Weighting Map Layers (Relative Importance)

Model weighting establishes the Model weighting establishes the relative importance among map relative importance among map layerslayers (model criteria) on a multiplicative scale (model criteria) on a multiplicative scale

The The Analytical Hierarchy Process (AHP)Analytical Hierarchy Process (AHP) establishes relative importance among by establishes relative importance among by mathematically summarizing paired comparisons of map layers’ importance. mathematically summarizing paired comparisons of map layers’ importance.

HD * 10.38HD * 10.38

R * 3.23R * 3.23

SA * 1.00SA * 1.00

VE * 10.64VE * 10.64

……group consensusgroup consensus is that housing density is very important (10.38 times more important than sensitive areas) is that housing density is very important (10.38 times more important than sensitive areas)

Generating Alternate Routes (changing weights)

The model is run using three The model is run using three different sets of weights for the different sets of weights for the map layers—map layers—

……to generate three alternative to generate three alternative routes routes (draped over Elevation)(draped over Elevation)

Summary and Conclusion

Use cartographical model to structure solutionsUse cartographical model to structure solutions Start with a ‘simple’ modelStart with a ‘simple’ model Add calibration or weighting model criteriaAdd calibration or weighting model criteria Apply model to simulate alternative scenariosApply model to simulate alternative scenarios Present a range of results to decision-makersPresent a range of results to decision-makers

ReferencesReferencesBerry JK, 2004. GIS Modeling, Part 5 Berry JK, 2004. GIS Modeling, Part 5 of Grid-based Map Analysis Techniques of Grid-based Map Analysis Techniques and Modeling Workshop,and Modeling Workshop, ASPRS Conference. ASPRS Conference.Berry JK, 2006. Berry JK, 2006. Map AnalysisMap Analysis. Online @ . Online @ www.innovativegis.com/basis