Hawth's Analysis Tools for ArcGIS

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 Summary

ZONAL STATISTICS ++ TOOL
Input: a continuous (numeric) raster layer, and a polygon layer
Output: results are written to a new DBF file
Features:

  • for each polygon this tool writes a stistical summary of the values in the raster layer that fall within the bounds of each zonal polygon (i.e. min, max, mean, standard deviation, and count)
  • if a polygon does not overlap a portion of the raster containing data (e.g. the polygon is completely filled with NoData cells), then "-999" is written to the fields in the output table to represent NoData
  • the FID of the polygon layer is added to the output table so that it can be joined back to the polygon layer
  • since the polygons are processed consecutively, overlapping polygons are allowed
  • the user can opt to only process selected polygons
  • perhaps most importantly of all, this code is written at a very low level, and does not require a Spatial Analyst license, and unlike the Zonal Statistics option in Spatial Analyst (8.x) there is no limit to the number of polygons that can be processed (hence "++")

Limitations:

  • this program will run slower if there are many, very large polgons
  • this program will fail if there are many large values in the raster (e.g. if the sum of pixel values for any polygon exceeds 2.1 billion (for integer rasters)


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 Help

Getting started. A polygon and raster layer must be loaded into ArcMap in order to use this tool. If the polygon layer does not contain a FID field and this program fails, it is suggested you convert it to a shapefile (as shapefiles are automatically provided with a FID field) or add a unique FID (feature ID) field to your polygon attribute table.

Naming convention for new fields. Field names are limited to 10 letters for DBF files. The new fields are named:
ZSTAT_MIN (minimum), ZSTAT_MAX (maximum), ZSTAT_MEAN (mean), ZSTAT_STDV (standard deviation), ZSTAT_CNT (count)

NoData cells. NoData cells are ignored in the calculation of Zonal Statistics ++.

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