[OSM-talk] Historical Data in OSM database

[Ed Avis]

Andrew Harvey <andrew.harvey4 <at> gmail.com> writes:

>Just a thought, perhaps for the time being one could add a changeset
>tag which says, this feature is being deleted because it is no longer
>there, but it was once there, to all changesets of deleation of
>historic features. Otherwise no one knows if the object was deleated
>because it was an error, or because it is no longer there.

That doesn't just apply to deletions.  If someone changes a road from
highway=unclassified to highway=track, does that mean it always was a track
but mapped wrongly, or does it mean the road surface has deteriorated?
Even additions of new objects have this problem.

In most cases you don't know.  You go out on a mapping trip and see that a
building is missing, but without specialist local knowledge you have no idea
whether it did exist in the past, or was just a mistake.

So I think such a tag could not be widely and reliably used.  It could only
be done in areas of very high quality map coverage where you can be pretty sure
that if a building was on the map in 2009, there was a building on the ground
in 2009, and vice versa.

-- 
Ed Avis <eda at waniasset.com>