How to do I drop certain overlapping features based on a set of conditions?

The next transformer will be an AttributeValueMapper to map the names to a priority value. So

Ancient Woodland = 1, Building Footprints = 2 etc

Then a Sorter to sort the features on _count first and Priority seconds. In Lowest to Highest order.

Then a Sampler to sample the first feature with Group By set to use the _count value.

Another approach, that makes use of list functionality.

• Make sure all polygons hava a unique number (use the UUIDGenerator to create one)
• Use the AttributeValueMapper to map the names to a priority value, as @Gary Nicholson​ proposes
• Perform an AreaOnAreaOverlayer, add the feature name, priority and ID attributes to a list
• Use a ListSorter on the priority attribute
• Use a ListIndexer to write the values of listitem 0 (feature name, priority and ID ) into the corresponding attributes
• Use a Dissolver on ID and feature name (or ID and priority) to combine adjacent objects with identical attributes
• Optionally add an Aggregator on ID and feature name (or ID and priority) to combine disjunct objects with identical attributes

See the attached workspace (based on the solution to this question) for a mockup.

The next transformer will be an AttributeValueMapper to map the names to a priority value. So

Ancient Woodland = 1, Building Footprints = 2 etc

Then a Sorter to sort the features on _count first and Priority seconds. In Lowest to Highest order.

Then a Sampler to sample the first feature with Group By set to use the _count value.

@Gary Nicholson​ any idea how I retain the areas that did not overlap?

Another approach, that makes use of list functionality.

• Make sure all polygons hava a unique number (use the UUIDGenerator to create one)
• Use the AttributeValueMapper to map the names to a priority value, as @Gary Nicholson​ proposes
• Perform an AreaOnAreaOverlayer, add the feature name, priority and ID attributes to a list
• Use a ListSorter on the priority attribute
• Use a ListIndexer to write the values of listitem 0 (feature name, priority and ID ) into the corresponding attributes
• Use a Dissolver on ID and feature name (or ID and priority) to combine adjacent objects with identical attributes
• Optionally add an Aggregator on ID and feature name (or ID and priority) to combine disjunct objects with identical attributes

See the attached workspace (based on the solution to this question) for a mockup.

@Gary Nicholson​ any idea how I retain the areas that did not overlap?

I would have used the ListSorter as well rather than exploding the list, but I didn't want to completely rewrite the workspace as @Hannah Wheldon​ was almost there.

As always with FME there are multiple ways to do things.