OSM Inspector/Views/Multipolygons

The Multipolygons view in OSM Inspector shows problems with Multipolygons.

Data sources

All data in this view is derived from OSM data.

Data for the whole world is available in this view.

Layers

The term convex hull is used as a shape that completely surrounds the multipolygon in question that is convex. This is generated by Geofabrik and will not be found in OpenStreetMap. It helps define where the problem is. The convex hull also includes the number of the relation, for example if there is a problem with relation 123456 it will be shown as text and can be viewed in the OpenStreetMap browser at http://www.openstreetmap.org/browse/relation/123456

Invalid Geometry

Often occurs when members of the multipolygon cross or touch each other. See Fixing OSMI self intersection for examples and suggestions.

One special case is when two rings in the multipolygon share an edge, for example two buildings that share a wall. Multipolygons are not meant to be used for this. If the buildings are in fact related, then a different relation type may be appropriate, for example "site" or "collection". Sometimes the relation can simply be deleted (the relation itself, not the ways it contains) if no meaningful data is lost by doing so.

Ring not closed

A ring in a multipolygon must be complete and without gaps. This unconnected end nodes show where the ring stops, this is a clue as to fixing the problem, however if the end node belongs to more than one ring end, only one ring will be shown in the data layer.

To fix this, it is often necessary to undelete (using Potlatch 1) a way that somebody else mistakenly deleted. Other times, an entire way (like a road or river) was included in the multipolygon, when only part of it should be - if so, then split that way, and remove the incorrect part from the multipolygon.

Role mismatch

Often occurs when a way with the "outer" role is labeled as "inner" or vice versa. If you have one large polygon with "holes", check that one of the holes is not actually outside the large polygon (in which case it should be "outer" not "inner").

type=boundary

OSM Inspector marks this as an error, assuming that the tag is deprecated as boundary=administrative is sufficient. However, this contradicts current best practices. See Relation:boundary and Relation:multipolygon. So this "problem" should be ignored.