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Not sure if it’s an issue as such, although I struggle to think of a scenario where you would want this functionality, and it might be obvious to some but just as an FYI

 

If you send multipolygons into a Dissolver with Aggregate Handling set to Deaggregate and choose attributes to sum, the polygons will be deaggregated first, this means that each constituent part inherits the attributes of the original multipolygon feature and this will then be summed to leading to unexpected values.

 

So from this

You get this

 

Good catch! I definitely have this in a few of my workspaces and definitely did not think of this scenario. Thanks for the heads up!

I guess it is generally good advice to do area/length calculations after spatial manipulation of whichever kind.

Just as your textbook example demonstrates!

I guess it is generally good advice to do area/length calculations after spatial manipulation of whichever kind.

Just as your textbook example demonstrates!

I’ve used area in this example, but in my case, I was summing other attributes that cannot just be easy recalculated post dissolve.

​@ebygomm This issue came up many years ago and at the time I think we just clarified in the documentation this limitation of the Dissolver regarding aggregates.  It should be able to get sums and averages from input features and not multiply by the number of elements within each aggregate.  I’ve filed FMEENGINE-87414 about this.

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