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 Read, design and implement a cartographical model Identify a logicalprocessing sequence Identify a logical processing sequence Calibrate and add weightings to model criteria Calibrate and add weightings to model criteria Simulate alternative scenarios and different perspectives 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. Transmission Line Routing Model Criteria – the transmission line route should… Avoid areas of high housing density Avoid areas of high housing density Avoid areas that are far from roads Avoid areas that are far from roads Avoid areas within or near sensitive areas Avoid areas within or near sensitive areas Avoid areas of high visual exposure to houses Avoid areas of high visual exposure to housesHousesRoads Sensitive Areas Houses Elevation Goal – identify the best route for an electric transmission line that considers various criteria for minimizing adverse impacts. Existing Powerline ProposedSubstation

7. 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 High Housing Density Far from Roads In or Near Sensitive Areas High Visual Exposure Avoid areas of…

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

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

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

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

12. Generating Optimal Path Corridors Pinch Point The alternative corridors are derived by considering the top 5 percent of the best routes within the project area …technique combines the Start and End preference surfaces to identify the overall preference for “forcing” routes off the optimal path

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

14. 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 1 for 0 to 5 houses …group consensus is that low housing density is most preferred 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.

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

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

17. 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 www.innovativegis.com/basis