[OSM-dev] Why are so many changeset so large?

[Andy Allan]

On 17 October 2012 13:53, Matt Amos <zerebubuth at gmail.com> wrote:

> getting to the point: this might to some extent mitigate the "large
> changesets" issue, as it would allow bboxes to be collected at a smaller
> granularity. however, it wouldn't be a full solution and we'd probably
> still need something like OWL to break down the geographic footprint of
> changesets further.

Further to this, I find this changeset extent "problem" is often
caused by looking at things the wrong way around. If you want to find
out what area the changeset covers, then we supply a bounding box to
help. However, if you want to know which changesets affect a given
area, this reverse question is much less easily answered. Hence OWL,
etc.

Beyond that, the extent is more of a promise that there are no edits
on the outside, rather than any guide to what's within. No changeset
completely fills, nor even evenly fills, its extent. There is a
widespread and very shakey assumption that smaller changesets are
somehow more likely to be rectangular or have a more even distribution
across themselves, but this won't hold in the real world in pretty
much any circumstances[1].

Basically, I see no need to worry about the extent of bounding boxes,
and no need to move to having bboxes on uploads instead of changesets
or other complications. No matter what we do, if your interest in a
changeset extends beyond the details of its extent, you need a
mechanism (again, e.g. OWL) to detail the actual locations of the
edits to the entities, and different interests (and different
entities) will have even have different buffers of interest around
them. Lets focus on things like that.

Cheers,
Andy

[1] Unless we all live in cities with north/south street grids and map
each city block in individual changesets :-)