On 04/13/2013 04:54 AM, Rovastar wrote:
As San Fran doesn't look like it has many railways I suggest you look at locations around the world maybe UK that has a detailed rail infrastructure so you get a better understanding about how it is done there.
Yes, I have looked at examples from elsewhere too; several of the examples in my proposal are actually from the UK.
The only consistent thing I see with railway tagging, regardless of where I look, is inconsistency.
To pick some examples from places I've lived or visited and am familiar with:
- The tramway along Damrak in Amsterdam is a two-way tramway in the middle of the street, just like my San Francisco examples. The tramway is a separate way from the highway here. However, elsewhere in Amsterdam, Ferdinand Bolstraat is a single way with both highway=unclassified and railway=tram .
- In Greater London, the London Underground Metropolitan Line crosses the LU Central Line and the Chiltern Main Line. All three of these railways are represented as one-way-per-track, which causes the data to suggest that the metropolitan line crosses under eight separate bridges, when in reality it's just two wide ones. Arguably this is a problem with the tagging scheme for bridges rather than for railways, but still.
- Continuing down the same line (pun intended!), at Finchley Road (heading towards central London) the Metropolitan Line and the Jubilee Line part ways in two separate tunnels, each with two tracks. The Jubilee Line is tagged as a single way representing the entire tunnel and both tracks, while the Metropolitan Line is tagged as two ways. I'd argue that it's sufficient to tag both as a single way, but if either one were to be separated it seems like the Jubilee Line is a better candidate, since it's a pair of narrow tunnels created with a tunneling machine, while the Metropolitan Line is a cut-and-cover pair of tracks running side-by-side in a wide tunnel.
- Moving on to England's main-line railways, the Great Eastern Main Line is tagged as a pair of ways from London to Whitham, but then it inexplicably becomes a single way at least as far as Manningtree (I didn't look any further, because I've never traveled past this point and so I have no idea what the railway looks like on the ground.)
So all that is to say that I think we're far from having a standard for tagging railways in Europe, too.
First and foremost I believe that more standardization would be beneficial to make the data more useful; currently the wiki says very little about how railways are to be tagged outside of talk pages and off-hand comments, and that leads to inconsistencies.
Secondarily I think OSM mapping should always *begin* with a simple ground transportation network (of highways, railways and waterways) and then build upon that with additional (optional) tagging schemes to add the level of detail that desired for more detailed rendering at close zoom levels and for less-common usecases like modeling the detailed operational details of a railway, both without conflicting with the basic use-case of a geo-spatial route graph.
My proposal achieves the simple network and *begins* the detail, leaving the door open for an interested party to continue it to whatever degree of detail the community finds useful, hopefully in a way that is compatible with approaches to also map highways and waterways in detail.
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