spatial analyst: cost distance analysis - esri · 2015-07-30 · what is cost distance analysis •...
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Spatial Analyst - Cost Distance Analysis Kevin M. Johnston
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Cost distance analysis - Outline
• What is cost distance analysis • The two step process • Adding complexity • Corridor analysis • Demo
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What is cost distance analysis
• One of the most common applications in Spatial Analyst • Euclidean distance – as the crow flies • Cost distance – as the phenomenon moves across the landscape • Based on cost
- Preference - Energy expended - Time - Dollars - Risk
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Problems addressed by cost distance analysis
• Constructing a road to a proposed shopping center • Conserving wildlife corridors between habitat patches • Supplying and reinforcing military troops in a deployment • Providing movement paths for fire fighters between posts • Locating a pipeline to connect energy fields to a refinery • Siting electrical lines
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Two step process for performing cost distance analysis
• Cost Distance tool - Input
- Sources – starting point - Cost surface – cost per map unit for travel
- Output - Cost distance – total accumulative least-cost for each cell to reach a source - Back link – direction to move from each cell to reach a source - Cost allocation – for each cell, which is the least-cost source
• Cost Path tool - Input
- Destination – ending point - Cost distance and Back link output rasters from Cost Distance tool
- Output - Least-cost paths – the least-cost path
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How to create cost surface
• Similar to creating a suitability model • Cost per map unit to move through
the cell • The lower the cost the better • Diagonal accounted for
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Step 1: How to perform the cost distance analysis The Cost Distance tool
• Sources
• Cost surface
• Output distance raster – for each cell, total least-cost to each cell to reach least-cost source
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Step 1: How to perform the cost distance analysis The Cost Distance tool (continued)
• Iterative approach
• Formula
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Step 1: How to perform the cost distance analysis The Cost Distance tool (continued)
• Back link
• Cost allocation
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Step 2: How to create the least-cost path The Cost Path tool
• Destination and the cost distance and back link output from the Cost Distance tool • Creates the least cost path from the destination to the sources
- Best single path
- Each zone
- Each cell
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Adding complexity Adding surface distance with the Path Distance tool
• Actual distance traveled • Endure the cost longer because going uphill
or downhill • Surface raster • The Path Distance tool
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Adding complexity Adding directionality with the Path Distance tool
• Adjustment to overcome going uphill and downhill
• Vertical factor - Surface raster endure cost longer - Vertical factor the additional cost to over come the
slope
• Horizontal factor - Additional cost to overcome a horizontal factor such
as wind
Accum_cost_distance = a1 + (((Cost_Surface(b) * Horizontal_factor(b)) + (Cost_surface(c) * Horizontal_factor(c)))/2) * Surface_distance(bc) * Vertical_factor(bc)
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Creating a cost corridor The Corridor tool
• Cost distance from source one
• Cost distance from source two
• Combine in the corridor tool • Extract by Attribute tool to identify acceptable
threshold
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Demo Cost distance analysis Creating a cost surface Cost Distance analysis Cost Path Adding complexity Corridor
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Conclusion
• Defining the cost units can be difficult • Identifying which sources and destinations to connect can be difficult
- Generally to closest (Euclidean) sources
• Cost does not account for - Difference modes of travel from a source - Starting costs - Dynamic adjustment – getting tired
• Creates the optimum least-cost solution - Assumes memory - Has visited all locations
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