I’ve been resolving OSM notes this past week and it’s been surprisingly engaging editing. I might try and sum up my pros/cons of the notes feature later but there was one particular problem that became a little project of its own that I want to explain a little more in depth here.

I came across notes by users didier2020 and jfire about parking lot duplicates in Washington DC. The problem was that some parking areas had multiple duplicate ways stacked on top of each other and shared the same nodes to define a single area. Because these areas were sharing the exact same features it’s pretty hard to spot the problem without specifically looking for it. Here’s what it looks like in JSOM:

When I first started on Didier’s note I spread out for a couple miles and kept finding the problem everywhere. Looking into the history of these ways it came back to an import of DC parking lots emacsen did in 2010. Here’s one of the changesets that make up the import: osm.org/browse/changeset/4118659. Now knowing that this affected all of DC I downloaded all the amenity=parking ways and checked it with JSOM’s validator. Here’s a recreation of what I saw (yellow is parking, red are duplicates):

JOSM’s validator can be a pretty great tool for solving lots of common problems but it can’t fix stuff like this on it’s own so I got started removing the duplicates from the top down. Once I got a reliable way of spotting them it was a simple process of keeping the cursor set to delete and clicking every way. Most only had one duplicate but many were stacked three or four high.

All in all it took about three hours, about 1,900 parking lots were deleted, the DC OSM file is a about 10mb smaller and there are now 6,166 parking lot ways in DC.