When uploading building footprints for Regina SK last week I had a bit of an oopsie. I had completely forgot that for very large uploads JOSM can finish uploading and close a changeset yet not reflect this in the UI. The result is that it looks like it is still uploading and will continue to show this forever. So I hit cancel and started the upload again, but limiting it to chunks of 10,000 objects. Then while waiting for that upload I looked at the slippy map, and the objects were already there, doh!

So I immediately cancelled the second upload, and downloaded the area in a new layer revealing tens of thousands of untagged duplicate nodes / ways representing building footprints. Fortunately it appears that JOSM first uploads the nodes / ways before applying any tagging to them, and I managed to stop the second upload while it was still uploading untagged objects. So I was able to use a JOSM filter (type:way

addr) to isolate the untagged buildings from the tagged buildings in the same position. Then I carefully removed untagged objects while avoiding anything valid the filter failed to hide.

A few times in the past I’ve come across huge swaths of untagged nodes, I guess this explains it.