Hawth's Analysis Tools for ArcGIS


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Input: two polygon layers (a “zonal” layer and a “summary” layer)
Output: attributes are added to the zonal polygon layer

  • for each polygon in the zonal layer, statistics are derived from the polygons in the summary layer that overlap that zonal polygon, and the results are written to new fields in the attribute table of the zonal layer
  • this tool works for complex polygons (donuts, etc)
  • this tool works with overlapping polygons in either/both layers
  • the user can specify to process only the selected zonal polygons (if any are selected)
  • two methods of summarisation are possible: area based summary, and attribute field based summary
  • area based summaries count the number and total area of the summary polygons that fall within the bounds of each zonal polygon (i.e. for the total area calculation, only the portion of the summary polygon that falls within the zonal polygon is counted)
  • attribute field based summaries allow the user to specify any number of attribute fields in the summary polygon layer that are used to generate any combination of the following statistics: area weighted mean, count, sum, min, max
  • various field naming conventions are available for the user to select
  • if the fields already exist, the user is given the option of overwriting them, or specifying a new (unique) field name prefix


  • the two polygon layers MUST be in the same projected coordinate system (this tool will not produce logical results if a geographic coordinate system is used)
  • this tool may not handle Null values in a Geodatabase correctly
  • this tool is designed to work with shapefiles, other formats have not been tested
  • due to a memory leak with ESRI’s spatial filters, this tool will gradually consume RAM – if all virtual memory is consumed then ArcMap will crash (this is only a problem for datasets with large number of polygons e.g. > 50,000)

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Getting started. Two polygon layers must be loaded into ArcMap in order to use this tool. If the user wishes to use the “Use selected features only” option, the zonal polygons must be selected before starting this tool.

Area based summary option. This tool produces two output attribute fields: 1) a count of the number of summary polygons that overlap each zonal polygon, and 2) a sum of the area of those polygons (but summing ONLY the portion of each polygon that falls within the zonal polygon). Note that summary polygons that share a common boundary with the zonal polygon, but which do not specifically “overlap” the polygon, are NOT counted. Note also that the area of each polygon is derived programmatically from the polygon geometry, NOT from a field called “Area” in the attribute table (if one exists). Thus the area estimates are influenced by the projection of the data.

Attribute field based summary. This tool produces up to five output attribute fields: 1) an area weighted mean of the values in the field specified (note that only the area of the summary polygon that falls within the zonal polygon is used in the weighting process), 2) a count of the number of summary polygons that overlap each zonal polygon, 3) a simple sum of all the summary polygon values that overlap each zonal polygon, 4) the minimum value of all summary polygons that overlap each zonal polygon, and 5) the maximum value of all summary polygons that overlap each zonal polygon.

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