Map bridges as areas

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After we imported sidewalks in #6 (in addition to manual sidewalk mapping in some cases), many highway overpasses ended up looking disjointed. To head off some misunderstanding from newer mappers who are unaware of OpenStreetMap’s physical separation rule and may not appreciate the need for sidewalks as separate ways, we can visually collect the lanes and sidewalks together by mapping bridges as areas. This is also an opportunity to correct any missing or mistagged crosswalks in the vicinity of these overpasses, which are locally significant for pedestrian routing.

Before	After

While we’re at it, the following public domain data sources provide the names, standard IDs, and a variety of other information about the bridges that we can add to OSM:

• State Highway Bridges (Caltrans, also available as a table in PDF format)
• Local Bridges (Caltrans)
• Roadway Bridges (San José Department of Transportation)

Bridge names and IDs are verifiable on ground. In California, every bridge has this information on a small sign or stamped onto a jersey barrier or column. However, in some cases, it has been painted over due to graffiti, and it’s usually in a place that’s hard to spot from Mapillary or Bing Streetside imagery. Highway overpass names typically don’t appear on maps, but that can be a distinguishing characteristic of OSM’s South Bay coverage.

The datasets above represent bridges as point features, so these bridge areas have to be mapped by hand. Since it is a completely manual affair, it isn’t necessary to follow the standard import proposal process, though we should cite Caltrans and the City of San José as sources.

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Coverage of bridge areas in the Bay Area is now concentrated in the South Bay, now that bridge areas have been mapped along several major freeways and streams:

openstreetmap-carto gives unusual prominence to San José’s SPUIs due to their overall surface area:

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• Roadway Bridges (San José Department of Transportation)

In addition to this Roadway Bridges layer, San José DOT also publishes a separate Bridges layer. The latter appears to include more attributes that aren’t as interesting to us, but otherwise I don’t know if there are any other relevant differences.