[Tagging] The actual use of the level tag

Tobias Zwick osm at westnordost.de
Wed Jan 30 13:44:50 UTC 2019


I stumbled upon a real-world example yesterday that may make the attempt
to have the level-tag describe a "global" order (as used in OpenLevelUp,
JOSM etc.) somewhat impractical -  with that level-selector UI element:

So, Hamburg is a really flat city. And even still, the mall "Europa
Passage" ...
https://www.openstreetmap.org/way/214840502#map=17/53.55223/9.99644
... does have two "ground floors". If you enter through the northern
entrance, you are in the lower ground floor (level=0), if you enter
through the southern entrance, you are in the upper ground floor
(level=1). If you walk alongside the mall though (Bergstra├če), there is
no (apparent) elevation.

So, imagine there are more indoor-mapped places both around the northern
and the southern end of that mall (there is, partly, but I am sparing
you the details), and as a matter of fact, sprinkled throughout the
entire city centre.
Then, to have a global order of things, the ground floor of all the
buildings South of that mall would need to be tagged with level=1 and
the ground floor of all the buildings North of this mall would need to
be tagged with level=0. In other words, must be relative to the level
order used in this building.

I see two problems with this:

1. Where to stop? How global is this global order? Going further South,
at what point does the level-value for the ground floor revert back to
0? What then if two such places collide? (A mall and a multi-level train
station were mapped separately and they built a tunnel to connect the
two, but they connect on different level=X - or not even a tunnel, let's
say they are just next to each other)

2. It is somewhat confusing for the user (and the mapper) because if you
look at such a map, at for example level=0, you would see an unexpected
split through the city centre where seemingly no building is
indoor-mapped South of that mall ... oh wait, it's all on level=1+.  ???

I, too, hope that the example was understandable.

Tobias



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