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
_______________________________________________ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
