[Imports] Criteria for matching objects for conflation

[Greg Troxel]

Perhaps before designing a language to express metrics it might be good
for people to come up with metrics (unconstrained in form) for several
use cases, and then try to summarize from that.   I don't have anything
concretely useful to add; this whole area is on my todo list rather than
my doing list...

My guess is that for point/point conflation, distance matters, and also
metadata (find point from GNIS and point not from GNIS that are
semi-close and share a name).

Then there's linear-way/linear-way, for matching streets in osm and
streets in another db (eg. TIGER, massgis).  That seems tricky since
it's not really the way that you want to match, but the aggegrate
geometry.  If an osm way is split and the other one isn't, that should
still match.  And of course polygon/polygon, which might be easier.

I suspect there's a node/way merge case, too.


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