Old style multipolygons

In the past multipolygons were considered valid also when they had their tags on the outer way (if there was only one such way or all ways had the same tags) while keeping the respective multipolygon-relation untagged. There is also a variant of old-style tagging where inner rings have the same tags as the outer rings.

This was deprecated and removed, and is necessary to support only when processing old data - before May 2017.

Nowadays it is considered a tagging mistake.

Implementation

• Implementation for compatibility – If relation is not tagged, the drawing style of outer ways is used.
  • If there is more than one outer way:

    The relation has tags

    Use the relation tagging. Ignore anything on the ways.

    The relation has no tags, but one or more constituting outer ways have an identical set of tags

    Valid data, take the tags from the tagged segments and apply them to the complete outer way.

    The relation has no tags, and constituting outer ways are tagged differently

    This is a problem situation with undefined results.

External links

• https://github.com/osmlab/fixing-polygons-in-osm
• https://josm.openstreetmap.de/ticket/10529 Visually deprecate old multipolygon styles- JOSM ticket
• https://blog.jochentopf.com/2017-08-28-polygon-fixing-effort-concluded.html Polygon Fixing Effort Concluded