[OSM-talk] Valid geometry for closed ways

[Sebastian Klein]

Hi,

what are valid geometries for closed ways that represent an area?

Surely overlapping line segments shouldn't be allowed, but what about 
ways that contain a certain node more than 1 time? (Except first and last)

Example:

A    B
x----x
|    |
x----x D--x E
C    |    |
      x----x
      F    G

The way would be [ABDEGFDCA].

An alternative would be to split it in 2 ways and use a multipolygon 
relation.

The question came up for the current improvements of JOSM's join areas 
feature (which can also fix self-overlapping ways):
http://josm.openstreetmap.de/ticket/5179


Sebastian