Issue a warning when multipolygon relations grow too large

[stephankn]

To avoid editing nightmares like the one described here:

​https://help.openstreetmap.org/questions/40792/editing-large-multipolygons-in-josm

it would be great if JOSM validator could warn early before polygons grow that large that it might be a good idea to split them into smaller parts.

[Klumbumbus]

What would be the requirement that a MP is "large"?

• numer of nodes?
• number of ways?
• number of inners?
• MP area?
• outer area?
• ...

[stephankn]

I don't think that for editing purposes the area itself is of concern.

It's probably a combination ob number of relation members (maybe start warning when more than 50 or 100) and total numbers of elements. I recently downloaded a large landuse polygon which cluttered the display while being incomplete (might be another ticket for not to fill incomplete polygons). That one fetched nearly 40.000 nodes with lots of ways involved. So a total number of Elements (nodes) of more than 5.000-10.000 also could trigger the warning.

[skyper]

For multipolygons without name JOSM could offer to only have one outer ring with the appropriate inner members and moving any other outer rings and their inner members in new relations for each outer ring.

See also #11164 where this method is also needed/used.

[pangoSE]

Replying to stephankn:

I don't think that for editing purposes the area itself is of concern.

It's probably a combination ob number of relation members (maybe start warning when more than 50 or 100) and total numbers of elements. I recently downloaded a large landuse polygon which cluttered the display while being incomplete (might be another ticket for not to fill incomplete polygons). That one fetched nearly 40.000 nodes with lots of ways involved. So a total number of Elements (nodes) of more than 5.000-10.000 also could trigger the warning.

Good idea. I support such a warning. The advantage of MPs is inversely proportonal to their size in nodes and members IMO.