Conflation workflow

[dkogan]

Is this our discussion forum? This isn't a bug report, but it needs to go somewhere.

I don't want to push too hard on my importing efforts before we get a better conflict resolution workflow or decide to give up on it. Regardless of that, there's much work to do to merge existing imported data. I just completed a nice chunk using the Conflation tool in JOSM. It takes a bit of work, but is fairly automated. This is a writeup of the workflow.

OSM changeset: http://www.openstreetmap.org/changeset/38260283
Task: http://labuildingsimport.com/project/2#task/618

The Conflation tool takes two sets of geometry on different layers, finds corresponding pairs of ways, and can update the geometry of the "Subject" layer with that of the "Reference" layer.

When the imported data was loaded in JOSM, here we had the good geometry, but bad tags in the "Data Layer"; this is the "Reference". The good tags are in the "buildings-addresses" layer; this is the "Subject". We need to select all the buildings in each layer separately, and configure the Conflation tool.

I used the Filter plugin to show only "building" objets. Then all of them can be selected at once. The nodes should be de-selected with Shift-u. These two selections can feed the Conflation tool.

We now run the Conflation tool. It spits out 3 sets of results: Matches, Reference Only and Subject Only. The Matches can transfer the geometry with the Conflate button. Since we deleted the building=yes tags, this happens automatically. We now have the good geometry in both layers.

Now we deal with the non-matched geometry.

The Reference-only list are the buildings that were found in the human-edited layer (good geometry, bad tags) that didn't have corresponding objects in the import. Almost entirely these are outside the bounds of this import set (but will be in-bounds for another set, so we'll deal with those later). There are three non-matching buildings within the bounds of the set. Those look like new buildings trace by the human. I left those, but removed all other in-bounds buildings from the Data layer because they will be replaced by the objects in the import layer.

The Subject-only list are the buildings preset only in the import. Most of these are potential backyard sheds and things manually removed. Some more are things are beyond the boundary of the original data set. I deleted all the backyard sheds from the import layer and left the out-of-bounds data, since it doesn't conflict.

I'm going to do all of these conflaty regions, unless somebody really wants to do it instead.

[maning]

@dkogan, Cool! I tried the conflation plugin while testing workflows for our import. I did not dig deeper as I'm confused with the terminology Match, Reference, Subject :)

If you can write step-by-step (with screenshots), that would be great especially as we approach areas with a lot of buildings traced by the community.

[dkogan]

Maning Sambale notifications@github.com writes:

@dkogan, Cool! I tried the conflation plugin while testing workflows
for our import. I did not dig deeper as I'm confused with the
terminology Match, Reference, Subject :)

If you can write step-by-step (with screenshots), that would be great
especially as we approach areas with a lot of buildings traced by the
community.

I went through the current task set (South LA), and completed all the
tasks with large conflations. The available tools really aren't very
good, and additional documentation wouldn't be very helpful. Each person
who wants to do this would need to work with it for a bit themselves.
During the next mapping meeting it would be useful to do an in-person
session for this.

I'm intending to do as many of these merging-heavy tasks myself as they
come up.

It would be most useful to smooth out the many warts in JOSM, but I'm
doing other things right now.