Hi Clay. I would use the layer=* tag to reflect the various elevations of the tracks in question, and probably offset them slightly from each other to make future editing easier.
-jack -- Typos courtesy of fancy auto spell technology. On May 4, 2020 2:15:07 PM EDT, Clay Smalley <claysmal...@gmail.com> wrote: >Hi all, > >Lately I've been tasking myself with mapping underground railway tracks >across the US, adding features like parallel tracks, crossovers, and >platforms wherever I can. My work includes the Market Street Subway in >downtown San Francisco and various lines in Philadelphia. I recently >began >doing this work on the NYC Subway—a huge system and a daunting task. >Fortunately, a local contributor (IsStatenIsland) has been working on >it as >well and we've had some friendly collaborative discussion. > >We're stumped on how to properly handle railways directly on top of >each >other. I've been able to avoid this issue for the most part, as it's >rare >in Philly (save some bits of non-revenue trackage) and the >double-decker >subway in San Francisco supports two railways with different gauges, >making >their centerlines differ by a few inches. But railways with identical >centerlines are a frequent occurrence in New York, with its various >configurations of local and express tracks. > >For example, the IRT Lexington Avenue Line (supporting 4, 5, 6, and <6> >trains) between 42nd and 103rd Streets, a length of about 3 miles, was >constructed as a double-decker cut-and-cover tunnel. In this case, the >express tracks lie directly beneath the local tracks. Currently this >segment is mapped on OSM as a single track with minimal detail [1]. How >should we go about adding these details? > >We've come up with some potential solutions, each of which seems to >have >its own drawbacks: > >1. Sharing nodes between levels, as in the Simple Indoor Tagging >schema. >This is the approach IsStatenIsland has taken, with a working example >at >the West 4th Street–Washington Square station [2]. >2. Duplicate nodes with identical positions. >3. Duplicate nodes, but positions scooched off-center a negligible >distance. This is how I mapped out Grand Central Terminal [3], with the >lower level mapped a foot or so away from where it should be. > >Personally, I'm leaning more towards #2. My qualm with #1 is that it >adds >intersections to the two overlapping levels of railways, which I find >misleading. And with #3 I worry that I'm mapping for the renderer. > >Thoughts? > >-Clay > >[1] https://www.openstreetmap.org/way/569345492 >[2] https://www.openstreetmap.org/node/597928309 >[3] https://www.openstreetmap.org/node/7099182377
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