[Talk-ca] GeoBase and Canvec import tools

[Richard Weait]

Dear All,

I was on the Imports conference call today.  There were callers from
seven countries with interests in dozens of data sets for all over the
planet.

One point that was raised by folks doing the French Corinne cadastre
import (landuse; tonnes of data) is that "bulk doesn't work".  Rather
than 48,000 nodes + 1,000 ways + 1,000 relations, they are breaking
uploads much smaller pieces.

Typically they prefer to limit a change set to:

Only one relation, it's included ways, and their required nodes.

This approach makes for many more change sets and each change set is
likely to be a single object of some sort.  They still have to break
these up further if the single relation is too big, but they aim for a
changeset of about 1,000 items total.

I'm finding frequent upload failures when dealing with changesets
larger than about 16,000 nodes.  Because of the nature of these change
sets, I can end up dropping thousands of unconnected nodes all over
the place.  Messy.  ;-)

One other approach that the French community is taking is to use
postGIS to detect objects that overlap similar objects that already
exist.  This is analogous to roadMatcher and it works on more object
types, directly in the (local) database.

There promises to be more information coming from the French community
and the rest of the import group in the next while.  I hope that those
in the Canadian community, particularly those developing tools can
consider these two approaches.

Best regards,
Richard