I had a close look on OSM multipolygon relations and how they are handled by OSM Editor. I hope this review may be helpful for development.
I see that Load OSM File creates one extra polygon feature per multipolygon relation. This conversion looks almost perfect on the geometry side, but (for me) doesn't work at all on the tagging side.
The way tags are attributes on its corresponding polygon or line feature. The relations tags are attributes on its corresponding polygon feature. I see no transfer of tags from the outer way to the (relations) polygon feature, even though I spotted a function
named MergeTagsFromOuterPolygonToRelation in OSMGPFileLoader.cs.
Have a look at
this OSM files, each contains one relation.
1246087 is an example where both the relation and the (one) outer way are tagged as landuse=residential. Result is one polygon for the outer way and one polygon with holes for the relation, both with attributes landuse=residential.
222876 has no landuse tag, the outer way is tagged as landuse=residential. Result is one polygon for the outer way with attribute landuse=residential and one polygon with holes for the relation without landuse attribute. Btw: The inner way 24887807 is tagged
as highway=pedestrian area=yes. It is represented as line feature, but should be a polygon feature.
1818497 is tagged landuse=residential, the various outer ways are without landuse tag. Result is one line for each outer way without landuse attribute and one polygon for the relation with landuse=residential. This kind of tagging is suggested in
OSM Wiki, and therefore the result in OSM Editor is best, too.
I think, while inner ways/isles usually are valid objects themselves, the features for outer ways should be omitted, attributes should go to the multipolygon features. At least, if the former would interfere with transfering back to OpenStreetMap, there
should be a clear mark in ArcGIS which features are not valid objects themselves. Btw it would be preferable to see if an osm_id is a way or a relation ID.
For a minor detail regarding the geometry look at relation
70884. There are three inner ways that each share a border segment with the outer way. These "holes" are not cut from the polygon feature shape.