Nominatim/Polygons

Error polygons list

As part of the import process nominatim validates and discards polygons which it considers broken for the following reasons:

Interior is disconnected	The inner ring of the polygon slices the outer ring into separate pieces
Duplicate Rings	The polygon contains multiple rings with exactly the same list of points
Self-intersection	The polygons overlaps with itself at a certain location
Ring Self-intersection	The inner and outer rings of the polygon touch at a certain location
Area reduced	The area of the polygon has been suddenly reduced by a significant amount - often indicates that one of more polygons from a multi-polygon are no longer valid although in some case this may be a false positive
Not a polygon	osm2pgsql was unable to create a polygon from the way or relation in a case where the tags indicated it should expect a polygon

The discards are logged to a table and can be viewed on the Mapquest Polygon Error List page.

This page provides a list of recent polygon errors with have not yet been fixed and is updated by the minute diff files so it should only ever my one or two minutes behind the live system. Details of the feature are shown (type,id,key,value,name,country) also with the error message. Where possible the error message links to the location on the map where the problems can be seen, although it should be noted that in some cases (particularly with Self-intersection) the error can be too small to be seen at zoom level 18 and will only be visible in a editor.

There are also edit links using josm (a direct link to download the object with the problem) or potlatch2 (only available where there is a specific location for the problem).