Tutorial on Least Cost Analysis by M Suhail

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Tutorial on Least Cost Analysis

By M Suhail

Objective: Find best route for oil Pipeline.

Input datasets:

1. Source of location/s or the point/s where the oil well is situated (source.shp)

2. Destination/s where the pipeline to be end (destination.shp)

3. Land Use Land Cover (.tif or any other raster format)

4. Digital Elevation Model (.tif or any other raster format)

Prerequisite softwares configuration:

Arc GIS 10 (Arc Editor)

Spatial Analyst (Activated) Criterions (hypothesis/s) for selection of Route/s are as follows:

Slope: higher Slopes are more costly than lower one

Land Use: land intervened by humans will be less costly than more intervened areas.

For example, farm land will be less costly than forest or dense settlement will be

high costly than transitional one.

Processing steps:

1. Add data as discussed above to the Arc GIS using Add button or via saved template.

2. Create tool box using Arc Tool Box

a. Steps are as follows: right click on Arc toolbox Add toolbox click on

New toolbox button on new window and named it as (least cost

path/route or whatever you need).

b. Now new toolbox will be added (see how on the below picture).

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3. Add Model to the new toolbox: right click on toolbox New Model

a. Then click on the model to prepare environment for cost allocation.

4. Select Model Properties: Go to model tab Model Properties

a. New Window will open as: Select the name and label (Least Cost path/route

or as per your wish OK

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5. Next step is go to environments tab and select the preference as: Check on boxes (a)

Processing Extent (b) Raster Analysis and (c) Workspace [if working with

geodatabase]. Then click on value button set the .gdb location (if applicable)

Processing Extent (default as dem_reclas.tif) Raster Analysis (cell size 90m or

DEM resolution) OK. Then final Apply and OK. And also save the model.

6. Now starts adding tools as require for model: Go to Spatial Analyst Drag and

Drop Slope tool from Surface tooltbar to the model workspace Double Click

on Slope Give input in to new window as dem.tif named the output as

dem_slope Output Measurement (optional) DEGREE and click apply, OK

and RUN.

7. Now classify dem into slope category: Again drag and drop Reclassify Tool from

Reclass tool of Spatial Analyst tool bar to the model workspace Double Click

on Reclassify Give input in to new window as dem_slope Click on Classify

button Classification window will open Select classification Method as

Quantile and give no. of Classes as 10 Give out put name as Reclassed_Slope

Click Ok, apply and then OK and RUN. (You will notice Old Value will be smaller

and their corresponding New Value also smaller respectively).

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Now Model Workspace will look like this:

8. Now Assign weight to the Land Use and Land Cover (LULC) layer with respect to

classified_slope layer: Again drag and drop Weighted Overlay Tool from Overlay

tool of Spatial Analyst tool bar to the model workspace Double Click on

Weighted Overlay set Evaluation Scale from 1 to 10 by 1 into new window

and click apply Add input layer (use + sign to add) as Reclassed_dem (give

Value into input Field) and click OK Repeat same steps to add another layer of

LULC (give Category or class into input Field) and Click OK.

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After adding both layers (LULC and Reclassed_Slope) the workplace will be look like this:

Now assign weights as per Hypothesis/s given above.

No change in Reclassed_Slope Layer as already classified while weighted value should

assign to LULC layer as per standard practice of weight value. For example least

important class with lower value and vice versa.

Select influence into % influence column as 40 per cent for LULC and 60 per cent for

Slope. Click on apply and OK button respectively. (Now model workspace will look like

this). Give output layer name as Costs and RUN the Overlay Analysis.

9. Now we will calculate direction of cost from source or oil well to destination: Go to

Spatial Analyst and click on Distance tool drag and drop Cost Distance tool to

the model workspace Double click on Cost Distance and give the input into

new window below as input raster or feature source data (give destination.shp

layer or pipeline end point), input cost raster (Costs), Output distance raster

(Output cost distance), and Output Back link Raster (Optional) [output backlink]

Click Apply, OK and RUN.

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Now Model workspace will look like this:

10. Now we will calculate final least cost path/route for pipeline construction: Again

drag and drop cost path tool from Distance in Spatial Analyst tool bar into

model workspace Double click on cost path and give the input into new

window below as input raster or feature destination data (give source.shp

layer), Destination Field (Optional) [OBJECT ID], Input cost distance raster

(Output cost distance), Input cost backlink raster (output backlink), and Output

raster (Least Cost Path) Click Apply, OK and RUN.

Exercise Finished: if you have any query please write at [email protected]
mailto:[email protected]

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Tutorial on Least Cost Analysis by M Suhail