[OSM-talk] osm2pgsql multipolygon parsing

[Eugene Alvin Villar]

On Sun, Sep 22, 2013 at 4:51 AM, Peter Wendorff
<wendorff at uni-paderborn.de>wrote:

> IMHO it's clear:
> - a tag on a way describes that way, if it's a closed way and the tag is
> describing an area, the tag matches the complete area inside that polygon.
> - if a way is outer of a multipolygon and there are tags on the way,
> these tags nevertheless describe the whole area, including all holes, as
> it's still a tag on the (simple) polygon.
> - if a way is inner of a multipolygon and there are tags on the way,
> these tags describe the polygon described by this way.
> - tags on the multipolygon relation describe the area represented by the
> relation - that is all outer polygons minus the inner polygons.
>

I agree that this is a good way of tagging multipolygons.

Unfortunately, many people don't tag multipolygons in this way. I've seen
people add building=yes to an outer way of a building with holes even
though there's a multipolygon relation with that tag already. It's most
likely that these people are not familiar with relations and they see an
outer way with no building=yes tag and decided to "helpfully" tag it.

Because of this, a more complicated interpretation of tags, such as
Frederik's, leads to less breakage (think rendering) and is more in line
with people's expectations.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/talk/attachments/20130922/8b8f8830/attachment.html>