[Talk-GB] Deletions and newbie editors

David Woolley forums at david-woolley.me.uk
Sun Oct 5 20:31:42 UTC 2014


On 05/10/14 21:00, Lester Caine wrote:

> and
> historic material would have an end date set which the renderers would
> also respect. A view of the data with any out of scope material
> suppressed is easy to implement, but at present we still don't have a
> reliable method of archiving material even if that involves transferring
> it to a separate copy of the whole database which can be used by
> historic rendering applications.

This part already exists, which it is one of the reasons why it is bad 
to do delete/re-add.  The data is archived in the live, online, 
database, now!

Whilst the archive exists and is accessible, what I'm not aware of is an 
API interface that allows one to retrieve the versions of objects that 
existed at a particular date.

That's also why deletions are particularly dangerous.  There is no easy 
way to find objects that used to exist in a particular area, whereas, if 
an object exists, you can search its back versions to backdate it.

There are some tactics you can use, like looking at back histories of 
relations, or recovering the changeset that created contemporaneous objects.

Unfortunately, editors can make it difficult to maintain the identity of 
an object, e.g. it is difficult to detach a node from a way without 
creating a low level delete/re-add.  Also, if you merge objects, you 
have to choose to maintain the history on just one of them, and getting 
the editor to choose one particular one is difficult.  (I think recent 
versions of JOSM may be able detach a node from a way.  The safest way 
of merging is possibly to do a paste tags, into the one you want to keep.)

The dates that apply here are the dates of mapping, not the the date the 
real world object came into existence, and there is no way of future 
dating.  Basically you can construct the map as of a date, but not a map 
of the world as of that date.








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