I would like to use FME to compare multiple polygons from a geodatabase. Namely, I would like to know where the polygons overlap, export this overlap area as a shapefile, and have the attributes of the new shapefile contain all information from both/all polygons which overlap.

I plan to use this workbench frequently in the future, so that each time I receive a new polygon, I can run it through the workbench and see which existing polygons it overlaps with.

I have tried using the AreaOnAreaOverlayer with a Tester set to _overlap>1. When I run this, it does shows me the correct shape polygon where the overlap is. However, I can't figure out how to get the attribute table to say which polygons it is that are actually overlapping. For example, if I read in "Red" and "Blue", the output will say "Red" with two overlaps, but won't mention the name of the other polygon ("Blue").

Just wondering what I am doing wrong - I am familiar with Esri products but have little experience using FME. I am essentially trying to recreate the Union tool.


1 Answer 1


I think you've pretty much got it, except you need to ensure the settings on your AreaOnAreaOverlayer for Attribute Handling are set to merge all incoming: enter image description here

I think once you've got that turned on, you'll have what you want.

But now that I reread this, are the names of the attributes all the same i.e. it sounds like you're reading just one table in and overlaying it on itself.

If that is the case, then you need to generate a "list" to hold all the values of the same attribute name that will accumulate in the overlapped area. You do this by turning on the List section in the AreaOnAreaOverlayer:

enter image description here

Of course, now that you have this list, you'll need to rename the parts of it into normal attribute names so that you can write to shape. Lists are powerful FME constructions but a bit tricky so I'd recommend checking out https://community.safe.com/s/article/working-with-list-attributes-tutorial and https://community.safe.com/s/article/transformers-for-working-with-list-attibutes (esp the ListIndexer) as you rename your "list" values into "regular" ones for output to Shape.

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