April 2011
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Spatial Joins failing where points fall on polygon boundaries!

Atlantic Ave & Ferguson Dr

Here is another question for you experts out there.

We have an ArcGIS Server service that performs identify commands.  Type in an address, get back the polygon that the address fall inside (Census Tract, etc).  Works nicely, except we found a recent issue regarding intersections.  Where an intersection (or geocode) also happens to be the exact location of a boundary between two polygons, we are getting a NULL response for the polygon.

An example is shown in the image.  This happens to be on the border of three different Census Tracts (even better).

 

 

 

I did some testing with various methods:

  1. In ArcMap, I used the Spatial Join by right clicking on the layer and the “Joins and Relates” – it failed.
  2. You know me – I went to ArcView 3.3 – it worked like a charm (of course!)
  3. I used the “Spatial Join” function in ArcToolbox – it worked.

If I added .005 feet to our output, then the join would work (5/1,000 of a foot).

So – what’s going on here?  Anybody have a workaround, since this is on ArcGIS Server and I don’t have the code.

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