[OSM-talk] railway=narrow_gauge

[Adrian Frith]

On Tuesday 19 June 2007 19:11:37 Nick wrote:
> We are getting tangled up in semantics!
>
> In South Africa, the standard gauge is 3ft 6in but it is called "Cape
> Gauge" or "Cap Gauge". "Standard Gauge" or "Stephenson Gauge" is always
> 4ft 8.5in.

Fair enough; my point is just that we must have enough data in the model to 
know, not only what the gauge of a railway is relative to "standard" 4' 8.5'' 
gauge, but also what the gauge is relative to the prevailing mainline gauge 
in the region. To render the entire Southern African railway network 
as "narrow-gauge railway" simply because it is narrower than "standard" gauge 
would be very silly. (After all, only 60% of the world's railways are 
standard gauge.[1])

And we want a solution that doesn't require different rendering rules for 
different parts of the world; at least, I assume we do, since it would make 
things like generating the slippy map a lot more complicated otherwise.

So given these semantic quibbles, I repeat my suggestion, slightly modified: a 
tag "gauge_rel" or something like that, with values "narrow", "normal" 
and "broad", which would indicate whether the railway in question was 
narrower, the same as, or broader (respectively) than the prevailing mainline 
gauge of the region. The assumed default would of course be "normal".

Perhaps the problem is that narrow-gauge railways are often drawn differently 
on maps because a railway being narrow-gauge usually indicates that it is 
special-purpose in some way: historical or touristic or funicular or only 
used by some specific industry. Generally, if a railway were just a normal 
part of the mainline network, it would long ago have been relaid at the 
prevailing gauge (barring special other circumstances).

So perhaps we need to analyse further *why* we might want to render 
narrow-gauge railways differently, and then add *that* data to the model?
Maybe just a "railway=special_purpose" value?

Regards,
Adrian

[1] http://en.wikipedia.org/wiki/Standard_gauge, lead paragraph
-- 
Adrian Frith
adrian at frith.co.za
http://adrian.frith.co.za/
+27 83 393 1257