Hawth's Analysis Tools for ArcGIS

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 Summary

PERCENT VOLUME CONTOUR
Input: a raster layer representing a probability density distribution (e.g. a kernel density raster)
Output: a set of percent volume contours
Features:

  • this tool creates contour lines representing the x% by volume contour (e.g. the 95% by volume contour)
  • this tool is also integrated into the Fixed Kernel Density Estimator tool and the Batch Fixed Kernel Density Estimator tool
  • this tool requires an ESRI Spatial Analyst or 3D Analyst extension license

Limitations:

  • this tool may fail with large rasters (e.g. > 7000x7000 pixels)
  • this tool outputs shapefiles only (no other vector formats are currently supported)


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 Help

Percent volume contours Note that a percent volume contour is not the same as the simple contours that are typically produced in tools like Spatial Analyst. A percent volume contour represents the boundary of the area that contains x% of the volume of a probability density distribution. A simple contour (like the ones that are produced in Spatial Analyst) represent only the boundary of a specific value of the raster data, and does not in any way relate to probability. For applications like animal home range delineation it is the percent volume contour that is required. The 95% volume contour would therefore on average contain 95% of the points that were used to generate the kernel density estimate.

Getting started You MUST ensure that you have a Spatial Analyst or 3D Analyst available before you start this tool (in ArcMap, see Tools > Extensions, and ensure there is a check-mark next to one of these extensions). A raster layer must be loaded into ArcMap in order to use this tool. The raster layer should represent a probability density surface, like a kernel density estimate.

Output folder Because this tool can generate many different output layers, the user is asked to specify an output folder (preferably a new, empty folder) so that the tool can automatically generate the output shapefiles. An empty folder will ensure that the program does not encounter naming conflicts with pre-existing shapefiles.

Naming convention The names of the shapefiles produces (one for each % value supplied) will be: PVC + the name of the raster + the percentage value.

Percent contour values You may enter any number of percent contour values as a comma delimited list, e.g.: 10, 20, 30, 90, 40, 75.68
Note that the numbers do not have to be ordered, and decimals are allowed.

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