Map AnalysisMap AnalysisProcedures and Applications in GIS ModelingProcedures and Applications in GIS Modeling

Topic 19, Routing and Optimal PathsTopic 19, Routing and Optimal Paths

Online book written byOnline book written by     Joseph K. Berry Joseph K. Berry   

www/innovativegis.com/Basis/MapAnalysis/www/innovativegis.com/Basis/MapAnalysis/

published bypublished by  BASIS Press  BASIS Press

Technical OverviewTechnical OverviewProcedures for Finding Optimal Routes and CorridorsProcedures for Finding Optimal Routes and Corridors

Transmission Line Siting Model Transmission Line Siting Model (Hypothetical)(Hypothetical)

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

Avoid areas ofAvoid areas of high housing densityhigh housing density ……prefer prefer lowlow housing density housing density

Avoid areas that areAvoid areas that are far from roadsfar from roads ……prefer prefer closeclose to roads to roads

Avoid areasAvoid areas within or near sensitive areaswithin or near sensitive areas ……prefer prefer farfar from sensitive areas from sensitive areas

Avoid areas of highAvoid areas of high visual exposure to housesvisual exposure to houses ……prefer prefer lowlow visual exposure visual exposure

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 and Optimal Paths Routing and Optimal Paths (avoid high housing density)(avoid high housing density)

ACCUMULATEDACCUMULATEDPREFERENCEPREFERENCE

SURFACESURFACE

EXISTINGEXISTINGPOWERLINEPOWERLINE

(START)(START)

Step 2.Step 2. Accumulated Accumulated Preference from the Preference from the existing powerline to existing powerline to all other locations is all other locations is generated based on generated based on the the Discrete Discrete PreferencePreference map. map.

MOST MOST PREFERRED PREFERRED

ROUTEROUTE

PROPOSEDPROPOSEDSUBSTATIONSUBSTATION

(END)(END)

Step 3.Step 3. The steepest The steepest downhill path from downhill path from the Substation over the Substation over the the Accumulated Accumulated PreferencePreference surface surface identifies the “most identifies the “most preferred route”—preferred route”—

Most Preferred RouteMost Preferred Routeavoiding areas of high avoiding areas of high

visual exposurevisual exposure

AVOID AREAS OF HIGH AVOID AREAS OF HIGH HOUSING DENSITYHOUSING DENSITY

Step 1. Housing DensityHousing Density levels (0-83 houses) levels (0-83 houses) are translated into values indicating relative are translated into values indicating relative preference (1= most preferred to 9=least preference (1= most preferred to 9=least preferred) for siting a transmission line at preferred) for siting a transmission line at every location in the project area. every location in the project area.

HOUSESHOUSES HOUSING HOUSING DENSITYDENSITY

DISCRETEDISCRETEPREFERENCEPREFERENCE

MAPMAP

(Least preferred)

(Most preferred)

Siting Model Flowchart Siting Model Flowchart (Model Logic)(Model Logic)

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

High Housing High Housing Density Density …build on…build on this single factorthis single factor

Far from RoadsFar from Roads

In or Near In or Near Sensitive AreasSensitive Areas

High Visual High Visual Exposure Exposure

Avoid areas of…Avoid areas of…“Algorithm” “Calibrate” “Weight”

Within a single map layer

Among a set of map layers

Siting Model Flowchart Siting Model Flowchart (Model Logic)(Model Logic)

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

Step 2Step 2

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

Step 2

Start

Step 3Step 3

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

Step 3

End

End

Start

Step 1Step 1

Identify overall Identify overall Discrete PreferenceDiscrete Preference (1 Good to 9 Bad rating)(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 1Step 1 Discrete Preference Map Discrete Preference Map

Calibrate

…then

Weight

HDensity

RProximity

SAreas

VExposure

<<click here click here to download an animated PowerPoint slide set to download an animated PowerPoint slide set describing calibration and weightingdescribing calibration and weighting >>

Step 2Step 2 Accumulated Preference Map Accumulated Preference Map

Splash Algorithm – like tossing a stick into a pond with Splash Algorithm – like tossing a stick into a pond with waves emanating out waves emanating out and accumulating preferenceand accumulating preference as the wave front moves 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 here click here to download an animated PowerPoint slide set to download an animated PowerPoint slide set demonstrating Accumulation Surface constructiondemonstrating Accumulation Surface construction>>

Step 3Step 3 Most Preferred Route 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 here click here to download a short video (.avi) describing Optimal Path analysisto download a short video (.avi) describing Optimal Path analysis >>

Generating Optimal Path CorridorsGenerating 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 to download an animated PowerPoint slide set demonstrating Optimal Corridor analysis>to download an animated PowerPoint slide set demonstrating Optimal Corridor analysis>

Example Results Example Results (Georgia Experience)(Georgia Experience)

Feature Article in GeoWorld, April, 2004Feature Article in GeoWorld, April, 2004

A Consensus Method Finds Preferred RoutingA Consensus Method Finds Preferred Routing See See www.geoplace.com/gw/2004/0404/0404pwr.aspwww.geoplace.com/gw/2004/0404/0404pwr.asp

Combining alternative corridors identifies the Combining alternative corridors identifies the decision space reflecting various perspectivesdecision space reflecting various perspectives

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

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

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

Fact Judgment

Calibrating Map Layers Calibrating Map Layers (using Delphi)(using Delphi)

Within a single map layer (criterion) …the “Greens”

……the process is the process is repeated repeated until there is “acceptable” until there is “acceptable”

consensus on the consensus on the CALIBRATIONSCALIBRATIONS

2) Each participant identifies 2) Each participant identifies their their cut-off valuescut-off values

1=good to 9= bad (avoid)1=good to 9= bad (avoid)

3)3) Summary statistics Summary statistics are are computed and used to computed and used to stimulate discussion about stimulate discussion about differences in opinionsdifferences in opinions

1) Information on each data 1) Information on each data layer is layer is presented andpresented and discussed discussed by the groupby the group

……structured method involving iterative use ofstructured method involving iterative use of anonymous questionnaires and controlled feedbackanonymous questionnaires and controlled feedback

Delphi Process Delphi Process (Spreadsheet)(Spreadsheet)

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

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

HD * 10.38

R * 3.23

SA * 1.00

VE * 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)

Weighting Map Layers Weighting Map Layers (using AHP)(using AHP)

Among a set of map layers (criteria) …the “Blues”

Conclusion Conclusion (Technical Overview)(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:References:

See See www.innovativegis.com/basiswww.innovativegis.com/basis, select , online book , select , online book Map AnalysisMap Analysis, Topic 19 “, Topic 19 “Routing and Optimal PathsRouting and Optimal Paths””

See See www.innovativegis.com/basiswww.innovativegis.com/basis, select Column Supplements, Beyond Mapping, September 03, , select Column Supplements, Beyond Mapping, September 03, DelphiDelphi

See See www.innovativegis.com/basiswww.innovativegis.com/basis, select Column Supplements, Beyond Mapping, September 03, , select Column Supplements, Beyond Mapping, September 03, AHPAHP

See See www.geoplace.com/gw/2004/0404/0404pwr.asp, www.geoplace.com/gw/2004/0404/0404pwr.asp, Feature Article in GeoWorld, April, 2004Feature Article in GeoWorld, April, 2004““A Consensus Method Finds Preferred Routing” (Georgia Experience)A Consensus Method Finds Preferred Routing” (Georgia Experience)