[OSM-talk] Historical Data in OSM database

[Frederik Ramm]

Hi,

David Murn wrote:
> OSM, by its nature, is excellent for retaining historic data, for
> example if a road is realigned, you have a history that shows how it was
> realigned, or if a road changes name, there exists a history of previous
> names.

I think that you, just as almost everyone else in this discussion, are 
wrongly mixing OSM's revision history and true on-the-ground history.

Revision history is there for the sole purpose of storing who has made a 
certain edit when. The time at which an edit was made has *nothing* to 
do with the time at which the object started or ceased to exist; the 
time at which an edit was made is the time when the existing object was 
first recorded, or when the object's destruction was recorded.

While revision history is nice to create animations about how the OSM 
data set grows, it is unusable for animations about what happened in the 
real world.

Properly modelling this would require adding an extra dimension to OSM 
where each property (tag, location) of an object could receive a 
validity timespan. Of course this would have to be in *addition* to the 
normal revision history - I would need to know that, for example, on the 
11th of November, 2010, someone changed the validity timespan for the 
attribute surface=cobblestone on a certain roman road to be 350-200 BC 
rather than 350-250 BC.

OSM revision history and on-the-ground history are orthogonal.

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"