San Francisco centerlines

More on Skunk Alley; I was talking to Eric F and he was saying it was a shame that this path wasn’t already in OSM. San Francisco publishes a shapefile of street centerlines; apparently when that was imported via TIGER into OSM they filtered out stuff that wasn’t quite a street, like unimproved rights-of-way. And indeed my second, southern segment of Skunk Alley is in that shapefile, as “UNNAMED 025” with CNN 19211000.

So that begs the question; what’s in the SF shapefile that’s not in OSM? Answering that question correctly requires a bit more geometric fiddling in PostGIS than I know how to do yet, but I did get a quick and dirty picture by using QGIS by drawing the OSM data in black on top of the SFData shapefile in purple. Anything purple peeking through is in the difference (roughly)

Lots of little snips and bits in the SF shapefile that aren’t in the OSM. Interesting! I should figure out how to use PostGIS to give me the actual difference.

While preparing this map I had to fix it so that Church street showed up. I used to draw everything with “railway is null”, but somehow that leaves out Church St. Maybe because it has a Muni track running down it? But with railways turned on you get things like underground subways (BART), the old abandoned track snaking through the Mission, etc. Haven’t found a reliable way to filter all that out yet; need to revisit HighRoad’s canned queries for that.