Map Analysis Procedures and Applications in GIS Modeling Topic 19, Routing and Optimal Paths Online book written by Joseph K. Berry www/innovativegis.com/Basis/MapAnalysis/ published by BASIS Press Joseph K. Berry www/innovativegis.com/Basis/MapAnalysis/BASIS PressJoseph K. Berry www/innovativegis.com/Basis/MapAnalysis/BASIS Press Technical Overview Procedures for Finding Optimal Routes and Corridors

Transmission Line Siting Model (Hypothetical) Criteria – the transmission line route should… Avoid areas of high housing density Avoid areas of high housing density …prefer low housing density …prefer low housing density Avoid areas that are far from roads Avoid areas that are far from roads …prefer close to roads …prefer close to roads Avoid areas within or near sensitive areas Avoid areas within or near sensitive areas …prefer far from sensitive areas …prefer far from sensitive areas Avoid areas of high visual exposure to houses Avoid areas of high visual exposure to houses …prefer low visual exposure …prefer low visual exposure HousesRoads 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

Routing and Optimal Paths (avoid high housing density) ACCUMULATEDPREFERENCESURFACEEXISTINGPOWERLINE(START) Step 2. Accumulated Preference from the existing powerline to all other locations is generated based on the Discrete Preference map. MOSTPREFERREDROUTEPROPOSEDSUBSTATION(END) Step 3. The steepest downhill path from the Substation over the Accumulated Preference surface identifies the “most preferred route”— Most Preferred Route avoiding areas of high visual exposure AVOID AREAS OF HIGH HOUSING DENSITY Housing Density levels (0-83 houses) are translated into values indicating relative preference (1= most preferred to 9=least preferred) for siting a transmission line at every location in the project area. Step 1. Housing Density levels (0-83 houses) are translated into values indicating relative preference (1= most preferred to 9=least preferred) for siting a transmission line at every location in the project area. HOUSESHOUSINGDENSITYDISCRETEPREFERENCEMAP (Least preferred) (Most preferred)

Siting Model Flowchart (Model Logic) 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 …build on this single factor this single factor Far from Roads In or Near Sensitive Areas High Visual Exposure Avoid areas of… “Algorithm” “Calibrate” “Weight” Within a single map layer Among a set of map layers

Siting Model Flowchart (Model Logic) Model logic is captured in a flowchart where the boxes represent maps and lines identify processing steps leading to a spatial solution Step 2 Generate an Accumulated Preference surface from the starting location to everywhere Step 2 Start Step 3 Identify the Most Preferred Route from the end location Step 3 End Start Step 1 Identify overall Discrete Preference (1 Good to 9 Bad rating) Step 1 “Algorithm” “Calibrate” “Weight” Within a single map layer Among a set of map layers

Most Preferred Discrete Preference Map Least Preferred …identifies the “relative preference” of locating a route at any location throughout a project area considering all four criteria [avoid areas of High Housing Density, Far from Roads, In/Near Sensitive Areas and High Visual Exposure] (most preferred) “Pass” “Mountain” of impedance (avoid) Step 1 Discrete Preference Map Calibrate …then Weight HDensity RProximity SAreas VExposure click hereclick here

Step 2 Accumulated Preference Map Splash Algorithm – like tossing a stick into a pond with waves emanating out and accumulating preference as the wave front moves Accumulated Preference Map (most preferred) “Pass” (most preferred) “Pass” …identifies the “total incurred preference” (minimal avoidance) to locate the preferred route from a Starting location to everywhere in the project area click hereclick here

Step 3 Most Preferred Route Optimal Route (most preferred) “Pass” (most preferred) “Pass” …the steepest downhill path from the End over the accumulated preference surface identifies the optimal route that minimizes traversing areas to avoid (most suitable) click hereclick here

Generating Optimal Path Corridors (most preferred) “Pass” (most preferred) “Pass” …the accumulation surfaces from the Start to the End locations are added together to create a total accumulation surface—the “valley” is flooded to identify the set of nearly optimal routes Optimal Corridor click here click here

Example Results (Georgia Experience) Feature Article in GeoWorld, April, 2004 A Consensus Method Finds Preferred Routing See Combining alternative corridors identifies the decision space reflecting various perspectives

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. 1 for 0 to 5 houses …group consensus is that low housing density is most preferred Fact Judgment Calibrating Map Layers (using Delphi) Within a single map layer (criterion) …the “Greens”

…the process is repeated until there is “acceptable” consensus on the CALIBRATIONS 2) Each participant identifies their cut-off values 1=good to 9= bad (avoid) 1=good to 9= bad (avoid) 3) Summary statistics are computed and used to stimulate discussion about differences in opinions 1) Information on each data layer is presented and discussed by the group …structured method involving iterative use of anonymous questionnaires and controlled feedback anonymous questionnaires and controlled feedback Delphi Process (Spreadsheet)

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 * R * 3.23 SA * 1.00 VE * …group consensus is that housing density is very important (10.38 times more important than sensitive areas) Weighting Map Layers (using AHP) Among a set of map layers (criteria) …the “Blues”

Conclusion (Technical Overview) GIS-based approaches for siting electric transmission lines utilize relative ratings (calibration) and relative importance (weights) in considering factors affecting potential routes. A quantitative process for establishing objective and consistent weights is critical in developing a robust and defendable transmission line siting methodology. Objective, Quantitative, Predictable, Consistent, Defensible References: See select, online book Map Analysis, Topic 19 “Routing and Optimal Paths” See select Column Supplements, Beyond Mapping, September 03, Delphi See select Column Supplements, Beyond Mapping, September 03, AHP See Feature Article in GeoWorld, April, 2004 “A Consensus Method Finds Preferred Routing” (Georgia Experience)