[OSM-talk] railway=narrow_gauge

[Laurence Penney]

Compared with roads, it's typically very easy to find out the exact 
gauge of any railway. As an example, in less than a minute I found out 
the gauge of the Ffestiniog Railway from their website: 22.5 inches.

So my vote is for:

gauge=22.5in (using 'in' or 'mm' as units)

We'd obviously not desire this key/value for "standard gauge" railways 
= 4ft 8½ in = 1435 mm.

http://en.wikipedia.org/wiki/Rail_gauge

-- L