# statistics by rectangle (raster image)

I have a shp file with some rectangles and I want to extract statistics within these areas from a raster image. I prefer ArcMap 9.3.

Your task could be done easily by using Zonal Statistics tool of Spatial Analyst extension.

• +1. This assumes the rectangles do not overlap, though. If they do overlap, you need to loop over the rectangles (or over subsets of disjoint rectangles). – whuber Jan 20 '11 at 16:58
• For versions of ArcGIS prior to 10, Hawth's tools has Zonal Statistics ++ which deals with overlapping polygons, give it a shot. spatialecology.com/htools/zonalstats.php – user681 Jan 20 '11 at 19:49

As a free alternative, SAGA GIS contains a module that may do what you want (Grid Statistics for Polygons). http://www.saga-gis.org/saga_modules_doc/shapes_grid/index.html

• +1. "Grid statistics for polygons" appears only to obtain a limited set of quantiles (5%, 10%, ..., 95%). However, the ability to obtain any quantile (apart from the median) does not exist in ArcGIS, so it's good to know about this capability. – whuber Jan 20 '11 at 17:01

You can also use GRASS for zonal statistics. From doc page:

r.statistics is a tool to analyse exploratory statistics of a "cover layer" according to how it intersects with objects in a "base layer". A variety of standard statistical measures are possible (called "zonal statistics" in some GIS).

The available methods are the following:

• distribution
• average
• mode
• median
• average deviation
• standard deviation
• variance
• skewness
• kurtosis
• minimum
• maximum
• sum

If you need more complex statistics or a free alternative (compared to spatial analyst), you can use raster package in R. From which you can extract pretty much any statistic you can imagine.