Spatial Join tool, sum of valus of features from join dataset not working

[JohnTangenberg]

I am having a problem with the Spatial Join tool (Tool box) at 10.0 SP5 ArcInfo, In the past I have used the tool to aggregate data from many small polygons to larger overlapping polygons through the field map  window setting the field to "Sum" and using JOIN_ONE_TO_ONE, resulting in a output that had the summation of the smaller polygons in the larger ones. In this case I am joining features "That have their center in" the Target feature.

Recent attempts at this have failed I end up with a join count of  1 and the values are not summed it only seems to count the 1st feature. my processing time is very short too so I know that it is not properly operating.

Attached is an image of the dialog box.

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John Tangenberg
GIS Analyst
Council for Watershed Health
700 N. Alameda Street
Los Angeles, CA 90012

[MatthewPayne]

Hi John,

The reason that "Have their Center In" does not give you the SUM of the smaller polygons is because this match option matches the join features if a target feature's center falls within them.  Basically put, if a larger polygon's centroid falls into a smaller polygon, that smaller polygon will be joined.  Here is the text from the help:

"HAVE_THEIR_CENTER_IN�??The features in the join features will be matched if a target feature's center falls within them. The center of the feature is calculated as follows: for polygon and multipoint the geometry's centroid is used, and for line input the geometry's midpoint is used."

So if you have an instance where there is not a smaller polygon existing where the larger polygon's centroid is, you would actually not get a match.  Hope this helps to clarify the behavior you are experiencing.

Matt