[Tagging] what does maxheight=none mean?

mmd mmd.osm+tagging at gmail.com
Mon Oct 27 06:27:19 UTC 2014

Tom Pfeifer <t.pfeifer at ...> writes:

> I stumbled over some maxheight=none tags on motorways, that did not even
> pass under a bridge. I found that this is the most frequent value of
> maxheight (2889 of 41474).


thanks for bringing this up. As the author of Maxheight Map ([1], [2]) I'd
like to put some of this discussion into perspective. Originally user
Win32netsky started a thread "Brückenhöhen eintragen in die OSM Karte" [4]
(adding maxheight infos to the OSM map) in the German forum, which attracted
more than 200k views and over 700 replies in the meantime. So this topic
already got quite some attention in the past, at least in Germany. To see
the huge momentum, visit the Wiki page [3] to see maxheight mapping progress
in Hamburg, Germany in the last four years.

We started to create the Maxheight Map arond 2 years back as a way to
support mappers in finding still unmapped bridges. At the same time, we were
looking for some way to express that there's no explicit maxheight
information (vulgo: no maxheight sign). The implicit limit as defined by
legislation would require a sign if the bridge is lower than < 4m
in Germany. For this purpose maxheight=none was invented to indicate that
there's no explicit maxheight limit. It was clear that the analogy to
maxspeed=none is somehow broken, but other ideas like maxheight=unspecified
didn't make it. We thought, well maxheight=none is here to stay.

Now enters JOSM: for some reason, they decided to create some rule to flag
maxheight=none as warning, as "none" is not a valid number. Suddenly mappers
started to remove those tags (JOSM must be right!). I picked this up in [4],
but it was sort of inconclusive. German OSM podcast "Radio OSM" discussed
this ('maxheight=none is bad'), but nobody really got the underlying idea.
Thanks a lot for Peter Miller's thoughts on this btw., that's exactly our

Following the "Radio OSM" story Martin K. started to invent
maxheight=unsigned and added this to the German wiki page without much
consultation/feedback from the community . I know "unsigned integers"
(=positive numbers), but unsigned maxheight seems a bit weird to me as a
non-native speaker. Maybe someone can chime in
here if this makes sense at all. Others started to propose
maxheight=default, which looks a bit better to me.

But again, we somehow need to start formalizing this a bit more, so that

- Mappers can be confident again to use the right tagging, that there's a
consensus to tag this stuff
  (after all if you look at the situation in taginfo and the actual numbers
for maxheight=none, the idea behind this tagging is really widespread and
commonly used by mappers!)

- JOSM no longer complains about maxheight=(not a number) and people stop
deleting those tags

Thanks for your time 


[1] http://maxheight.bplaced.net
[2] http://wiki.openstreetmap.org/wiki/Maxheight_Map
[4] http://forum.openstreetmap.org/viewtopic.php?id=14154
[5] http://wiki.openstreetmap.org/wiki/User_talk:Dieterdreist#maxheight

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