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Grid-based GIS Modeling

Grid-based GIS Modeling. Nigel Trodd Modified from Berry JK, 2004. GIS Modeling, presented at Grid-based Map Analysis Techniques and Modeling Workshop, ASPRS Conference. Aim and Objectives.

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Grid-based GIS Modeling

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  1. Grid-based GIS Modeling Nigel Trodd Modified from Berry JK, 2004. GIS Modeling, presented at Grid-based Map Analysis Techniques and Modeling Workshop, ASPRS Conference.

  2. Aim and Objectives By the end of this lecture you should better understand the process of map analysis. You should be able to: • Read, design and implement a cartographical model • Identify a logicalprocessing sequence • Calibrate and add weightings to model criteria • Simulate alternative scenarios and different perspectives

  3. 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)

  4. Communicating Model Logic (suitability)

  5. Decision Support Systems Framework User-interface Model DB

  6. Existing Powerline Goal– identify thebest route for an electric transmission linethat considers various criteria for minimizing adverse impacts. Proposed Substation Houses • Criteria – the transmission line route should… • Avoid areas ofhigh housing density • Avoid areas that arefar from roads • Avoid areaswithin or near sensitive areas • Avoid areas of highvisual exposure to houses Roads Sensitive Areas Elevation Houses Transmission Line Routing Model

  7. Avoid areas of… High Housing Density Far from Roads In or Near Sensitive Areas High Visual Exposure Routing Model Flowchart(Model Logic—components) Model logic is captured in a flowchart where the boxes represent maps and lines identify processing steps leading to a spatial solution

  8. Step 1 Identify overall Discrete Preference (1-9 rating) Step 2 Generate an Accumulated Preference surface from the starting location to everywhere Step 3 Step 2 Step 1 Step 3 Identify the Most Preferred Route from the end location Routing Model Flowchart(Model Logic—maps) Model logic is captured in a flowchart where the boxes represent maps and lines identify processing steps leading to a spatial solution

  9. AVOID Least Preferred Most ATTRACT EXCLUDE (0) …average of the four individual preference maps for overall preference at each cell Step 1Discrete Preference (friction) Map … identifies the relative preference (friction) of locating a transmission line through any cell of the project area considering multiple criteria

  10. Cumulative cost surface Step 2Accumulated Preference Map … identifies the preference to construct the preferred transmission line from a starting location to everywhere in a project area

  11. Preferred Route Preferred Route Step 3Most Preferred Route (least-cost path) … the steepest downhill path over the accumulated preference surface identifies the most preferred route — minimizes areas to avoid

  12. Rankings Weights …but what is high housing density and how important is it? …etc? Siting Model Flowchart (Calibrating and Weighting) Model logic is captured in a flowchart where the boxes represent maps and lines identify processing steps leading to a spatial solution Avoid areas of… High Housing Density Far from Roads In or Near Sensitive Areas High Visual Exposure

  13. 1 for 0 to 5 houses …group consensus is that low housing density is most preferred Calibrating Map Layers(Relative Preferences) Model calibration refers to establishing a consistent scale from 1 (most preferred) to 9 (least preferred) for rating each map layer The Delphi Process is used to achieve consensus among group participants. It is a structured method involving iterative use of anonymous questionnaires and controlled feedback with statistical aggregation of group response.

  14. …group consensus is that housing density is very important (10.38 times more important than sensitive areas) HD * 10.38 R * 3.23 SA * 1.00 VE * 10.64 The Analytical Hierarchy Process (AHP) establishes relative importance among by mathematically summarizing paired comparisons of map layers’ importance. Weighting Map Layers(Relative Importance) Model weighting establishes the relative importance among map layers (model criteria) on a multiplicative scale

  15. The model is run using three different sets of weights for the map layers— …to generate three alternative routes (draped over Elevation) Generating Alternate Routes (changing weights)

  16. Summary and Conclusion • Use cartographical model to structure solutions • Start with a ‘simple’ model • Add calibration or weighting model criteria • Apply model to simulate alternative scenarios • Present a range of results to decision-makers References Berry JK, 2004. GIS Modeling, Part 5 of Grid-based Map Analysis Techniques and Modeling Workshop, ASPRS Conference. Berry JK, 2006. Map Analysis. Online @ www.innovativegis.com/basis

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