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I'm new to python and arcpy but I've been trying to learn how to run geoprocessing tools using arcpy. I have (for this example) 2 shapefiles, a and b, which are both polygons. From plotting them in arcMap, I know that b is found entirely within a.

I would like to write a script that will take these two shapefiles and give me a True/False response about whether or not one polygon contains the other. I was thinking of using the arcpy.Geometry.contains() function.

I have the following:

>>> a_shp="C:\\Data\\shapefile_a.shp"
>>> b_shp="C:\\Data\\shapefile_b.shp"

>>> #read in as geometry
>>> a=arcpy.CopyFeatures_management(a_shp, arcpy.Geometry())
>>> b=arcpy.CopyFeatures_management(b_shp, arcpy.Geometry())

>>> arcpy.Geometry.contains(a[0],b[0])
>>> arcpy.Geometry.contains(b[0],a[0]) #maybe I got the order wrong? Trying the other order

>>> #Maybe I'm getting the syntax wrong, trying something else
>>> a[0].contains(b[0])
>>> b[0].contains(a[0])

I get no error messages but clearly something isn't working properly. Am I doing this right? Any pointers would be greatly appreciated. Thank you!

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This strategy should work as well as Jason Scheirer's method. I have used geometry object outputs before. Did you get the correct output from Jason's method? The correct syntax is a[0].contains(b[0]) or conversely b[0].within(a[0]). I am not certain though that you can reference by subscripting on a geometry list. –  blord-castillo Oct 10 '11 at 11:08
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migrated from stackoverflow.com Oct 10 '11 at 10:52

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1 Answer

up vote 3 down vote accepted

a and b will be result objects in this case. You'll need to open two search cursors and pull the shape field off of each to use the contains operator. Something like this:

for row1 in arcpy.SearchCursor(shapefile1):
    for row2 in arcpy.SearchCursor(shapefile2):
        if row1.shape.contains(row2.shape):
            return True
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Thanks Jason! That works! I guess I just need to get a better understanding of arcpy... –  user983332 Oct 7 '11 at 19:16
These helpfiles should be helpful: –  blord-castillo Oct 10 '11 at 10:58
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