[OSM-talk] Zonal restrictions.
osm at tobias-knerr.de
Wed Apr 29 20:15:52 BST 2009
Kurt Roeckx schrieb:
> I'm looking for a way to map restrictions for a zone. This
> includes things like maxspeed, maxweight and parking restriction.
> I want to avoid having to place those tags on all the roads inside
> the zone, specially for large zones, since it's very easy to forget
- if you use tags to mark a zone, you can forget them just as easily
- adding all ways to a relation isn't easier than tagging all of them
- if you mark the entrances of the zone, you (or someone adding a track
leaving the zone) can forget an entrance, which is much worse than
forgetting a single tag because this error might affect areas far
outside the zone
- polygons indeed can save work, but suffer from problems e.g. with
The advantages of zonal mapping for quality are, however, only minor.
Forgetting a tag on a single way isn't that much of a problem. It will
either have only minor effects or be easily spotted by someone. This, in
my opinion, isn't enough to compensate for the potential problems:
- zonal mapping can be harder for newbies to understand, depending on
editor support. Making simple road attributes hard to understand is a no-go.
- zonal mapping makes it more difficult to write software evaluating the
information, so less people will be able or willing to create cool stuff
with OSM. Those who still do will have less time for other features.
- some options for zonal mappings (such as polygons) have performance
disadvantages. This makes providing OSM services more expensive or
causes slower software.
Therefore, I suggest that you map zones _in addition_ to directly adding
tags with the information to the streets. This serves your stated
purpose of avoiding errors: Zone information can be automatically
compared with tag information to make sure that all streets in the zone
have the required information. It would even be possible to create
editor plugins for the task of adding the zone's tags to the streets
inside it on demand.
Most of this applies primarily to small-scale zones. I don't suggest
that everyone uses tags to define which country an object is in. The
built-up areas are probably a border case. I'm not entirely sure whether
tagging of individual highways is a good option here. It might still
be, though, because it can also serve as a "I have checked for explicit
access restrictions (such as maxspeeds) and there are none" marker.
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