[Tagging] Feature Proposal - RFC - More Consistency in Railway Tagging

Tobias Knerr osm at tobias-knerr.de
Sat Apr 13 17:36:09 UTC 2013


On 13.04.2013 08:11, Martin Atkins wrote:
> http://wiki.openstreetmap.org/wiki/Proposed_features/Railway_Schematic_Mapping

You are touching a tricky issue with a proposal that is honest about its
limitations, so I welcome the constructive input. But unfortunately, I
doubt it is the right way to go.

First, lets compare this to highway: There we map separate highway ways
when there is a physical separation, e.g. with dual-carriageway
motorways. This is not the same as lanes, where you may often change
lanes at any time e.g. for overtaking, and could often move to any lane
even if you are not allowed to. Between railway tracks, there is
*always* some physical separation - you cannot just move to a parallel
track. So it is not true that your proposal would be required to
maintain consistency with highways.

Applying a "lanes" tagging scheme to railway would just highlight its
limitations: Even with highways, we don't have any established solution
for transitions between way segments with different lane layouts yet. As
you admit in your proposal, this means that we would, for example, lose
our current ability to to easily and intuitively map railway switches.

There would many similar unsolved issues regarding accuracy, many of
which you actually point out yourself, too (such as the 90° turns at
intersections). But I think not all mappers would agree with your
judgement that this very generalized mapping is good enough. Too much
important detail is "left as an exercise for someone else who is
interested".

Therefore, it is not surprising that mapping of individual tracks tends
to dominate in well-mapped areas with decent aerial imagery. At least in
the areas I'm familiar with, drawing parallel railways as a single way
is mostly limited to two cases:
* early mapping (sometimes even GPS based), to be improved later
* trams, as the unsolved rendering issues are particularly obvious there

To sum this up: I'm aware that we have unsolved problems with our
railway mapping scheme, and that it is hard to serve the needs of many
different use cases at once. But your proposal feels like giving up and
focusing exclusively on a generalized, road-centric map, and we should
strive for more than that.

Tobias



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