OSM (Multi)Polygon Statistics
This page shows several statistics related to multipolygons over time.
Multipolygons created from relations
The number of multipolygons created from relations with type=multipolygon or type=boundary.
Multipolygons created from closed ways
The number of (multi)polygons created from closed ways. Tags are not taken into account (except area=no), so this also includes closed ways that are not actually polygons, such as roundabouts or so.
Nodes in multipolygons
The total number of nodes in all multipolygons (created from relations or ways).
Old style multipolygons
The number of multipolygon relations that have no tags (or only unimportant ones like created_by) on the relation and have their tags on the outer way(s) instead. This old style tagging is deprecated.
The percentage of all multipolygon relations that have old style tagging.
Multipolygon relations or ways with self-intersections of the way or ways involved. These are broken and need to be fixed. The number reported here is the number of crossing segments. Because you always have at least two segments involved in an intersection, the number of affected (multi)polygons is about half this size.
Errors: Duplicate nodes
Multipolygon relations or ways with consecutive indentical nodes or multiple different nodes at the same location. These are usually fixed while post-processing the multipolygon, but it is still better to fix them in the data.
Errors: Duplicate segments
Number of segments (a segment is a connection between two nodes) that appear multiple times in the border of a multipolygon relation or way. This is often, but not always wrong.
Errors: Open rings
Multipolygon relation where the outer or inner border is not closed. This is always an error and needs to be fixed.
Errors: Inner rings with same tags as outer rings
Some multipolygon relations have the same tags on outer and inner ways or the relation and inner ways. This is deprecated. Multipolygon tags should be on the relation only, outer ways are usually not tagged at all (unless they constitute an object in their own right), and inner rings either have no tags or their own tags if they constitute an object in their own right.
Errors: Wrong role
Multipolygon member roles other than empty, outer or inner or where the tagged role is not the correct one. This reports the number of segments which have a wrong role, not the number of ways or relations. That's why this number is so large.