[OSM-talk] Potential problems moving/depreciating map features tags.

David thewinch at gmail.com
Fri Jul 13 18:52:44 BST 2007


With all the talk of fixing the inevitable inconsistencies and niggles
in map features I haven't seen much talk on the potential problems
that changing tags could cause.

I think it would be wise to discuss this a bit. The problems I see follow.

1. How will the changes be communicated? Both to mappers entering data
and consumers of the data either via the API or planet dump. If people
don't know the tags have changed they will keep using the old ones.

I believe I read on one of the lists there are more active mappers
that are not subscribed to the various mailing lists than are
subscribed.
I also think the map features wiki page may not be viewed often by
lots of mappers. Once you memorize the basic tags you need you don't
have a lot of reason to go back. If you do it's possibly just to find
a new tag you haven't used yet so you might easily skip over the
changes without noticing them.

Also the planet dump is easy to get hold of and in a relatively simple
format. This means it's very easy to use without making any noise.
Lots of people could be using it for all sorts of things without
anybody knowing.

Perhaps it would be better to pool the changes together and apply them
all at once with lots of fanfare to increase the chances mappers will
notice.

2. User inertia. Even for technical people getting the hang of mapping
can be a bit of a challenge. Since the old tags will presumably
continue to work many people might just continue using them instead of
making the effort to learn new tags.

3. What to do with the old tags in the database? The old tags can't
really be deleted because the person entering them might be using a
different tagging scheme.

The new tags could be added to primitives that have the old tag. That
has the disadvantage of increasing the size of the data without
conveying additional information.

Just ignoring the old tags sort of gives a situation I feel map
features was intended to avoid. Having different tags with the same
meaning.

The old tags are not too bad if a tag gets changed once but what after
two, three or four times? Using the data starts to get more difficult
as you need to be away of not only the current tags but all the
historical ones as well.

Presumably at some point in the past the tags currently depreciated
fit into the tagging scheme reasonably well. As map features continues
to grow and evolve more tags may look out of place including those
previously moved.  So having tags move more than once isn't out of the
question.

I personally think it may be best to live with the inconsistencies.
The infrastructure isn't currently there to support the amount of
evolution it needs to stay consistent. I think it may need to move
beyond a wiki page and become more integrated with the api. Perhaps
even to the point map features tags are separated from the rest of the
tags and expected to comply with a defined standard. That way editors
like JOSM could present the standardized tags to the user anyway they
wanted. Hiding any inconsistencies or even the concept of keys and
values altogether.

Ok so I rambled at the end but I think the earlier points have at
least some merit.

-- 
David




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