Calculation of least cost paths in networks

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Calculation of least cost paths in networks
Various ways to get from one point to another
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Calculation of least cost paths in networks

• One must search through a large number of
  possible solutions for the optimal solution
• (the one that optimally satisfies the given
  criteria)
• optimization algorithms come in many forms based
  in artificial intelligence or other heuristics

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Least-cost paths in raster data sets
One use of raster data that is difficult to do
in vector polygon data is least-cost path
analyis Different themes can be used to give
various information about the relative ease of
traversing
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Example path from Logan to Tony Grove
Given the road network, the road does not appear
to be the shortest way to get there
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Example path from Logan to Tony Grove
Given the road network, the road is not the
shortest way to get there
The road choice makes more sense when
considered in terms of topography
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Example path from Logan to Tony Grove
Some landcover types are easier to cross than
others
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Example path from Logan to Tony Grove
All else considered, steeper slopes are harder to
cross than shallower
Imagine route that attempts to keep on lighter
colored pixels (shallower slopes)
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Example navigating ridges on hills
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Example navigating ridges on hills
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Example navigating ridges on hills
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Example finding boat paths
Started with project where embarkations (origins)
and destinations of recreational boaters were
gathered from telephone surveys The problem here
was to find the most likely path between origins
and destinations it was assumed that boats would
take the easiest, or least-cost path to their
destinations
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Example finding boat paths
Every factor that affects where boats choose to
go was given a relative cost numbers were
initally arbitrary (educated guess) numbers were
adjusted until the paths reflected real boater
paths
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Reclassification
Reclassification was used in the previous example
Depth originally continuous coverage from 0 - 25
ft after reclassification, two classes gt draft,
lt draft
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Reclassification
Reclassification was used in the previous example
Shoreline converted from discrete polygon
coverage to continuous grid (grid cell value
function of distance to shore)
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Reclassification
Reclassification was used in the previous example
Seagrass and ICW routes retained shape, but
changed attributes
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Class Project

• Your task
• Use GIS, and the knowledge you have gained thus
  far, to solve a problem
• Problem should have some spatial aspect
• It can also have some aspect of your professional
  interests
• present the results of your project in a final
  report

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Class project

• Final report
• Post on web page, same as assignments
• Start with description of problem to be solved
• Give a review of how GIS has been used in this
  field in other cases
• Describe your data sources
• Describe your methods
• Show results of analysis
• Discuss conclusions

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More on the class project
You are encouraged, though not required, to work
in groups
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Examples of past projects

• Identifying which wetlands are most in danger
  from urban expansion in cache county
• Identifying habitat for noxious weeds in Camp
  Williams
• Creating a bottom contour map for a stretch of
  the Blacksmith Fork River
• Evaluating hazards from a failure at Porcupine
  Dam
• Modeling habitat for beetle infestations in Utah
• Spatially referencing a road surface database for
  Utah
• Change detection of forested areas in Morocco

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Next homework assignment

• Describe your project idea
• Problem statement
• Potential data sources
• Possible methodologies