I am validating shapefiles polygon geometry using shapely, and have also attempted it using FME. Some polygons return the error "Nested Shells".

I cannot find a definition of what the problem is, whether in FME documentation (here) or in google search results on shapely or OGC geometry validation.

Would anyone have a definition or (ideally!) a graphic example?

1 Answer 1


A Nested Shell is a polygon on top of another polygon.

Nested shell

Image source

  • 1
    OK, many thanks!! It sounded to me like something way more complicated, but this is easy to address.
    – Hélène
    Nov 25, 2015 at 8:47
  • 1
    What did you end up doing to address this? Oct 12, 2021 at 0:03

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