I am trying to perform a spatial join that will aggregate about 90 fields using a SUM function.

In the Field Map I get the option to right click on each field and set the merge rule to SUM.

This would be extremely tedious for me to do, especially since I have to perform such a spatial join for 30+ layers.

Is there a way to change the "default" merge rule option to SUM instead of FIRST? How about change the field merge rules in bulk?

Screenshot to illustrate the point

Field Map List

  • Can you provide screen shot of the fields you are look to aggregate?
    – hannbroo
    Feb 15, 2017 at 19:06
  • 1
    @hannbroo added screenshot in post Feb 15, 2017 at 19:17
  • I thought there would have been an environment setting for this, but I don't seem to be able to find one. Could probably be done with a bit of arcpy, although field mappings in arcpy can be tricky too
    – Midavalo
    Feb 15, 2017 at 19:34

1 Answer 1


I think you should look at an alternative workflow which involves these untested steps:

  1. Spatial Join (or Union if dealing with overlapping polygons)
  2. Summary Statistics
  3. Join Field
  • My problem is that the spatial join step requires manual input of merge rules for each field individually (please refer screenshot above) Feb 16, 2017 at 6:22
  • This suggestion would not use merge rules of Spatial Join. That logic would be in the Summary Statistics. At the moment I am putting this forward as an idea without being 100% clear about what you are trying to do.
    – PolyGeo
    Feb 16, 2017 at 7:40
  • I am trying to "add" overlapping polygons, each of which has the fields above, to create a layer holding the cumulative total. The problem with Summary Statistics is that it doesn't take spatial location into account, so I would have to perform a spatial join with a temporary grid to assign unique IDs to each polygon, and then perform the summary statistics with the unique ID as "case". That is also rather tedious. Feb 16, 2017 at 7:47
  • You made no mention of overlapping features in your question but, in any event, I think Summary Statistics on a Union-ed feature class will give some useful data to work from but ArcPy cursors may provide more flexibility if you need it.
    – PolyGeo
    Feb 16, 2017 at 8:08
  • Yes, I didn't think it was necessary since all I needed was to set Merge Rules in bulk. It was my understanding that Union will discard the fields of join features that overlap if they are identical to the target features, or am I missing something? Summary Statistics would then only be performed on the original data set, which is of no use. Feb 16, 2017 at 8:20

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