Other Scales and Gauges
Archive from about 2003: Last updated Apr 2016. (most links are no longer operational)
Other Garden Railway Scales
Big Scale, Small Space?

There's a lot more information on this Gn15 website.
For those interested in constructing "Micro Layouts", there are examples and plans available from Carendt.com
Scale: ~1:20th
Gauge: 18mm (representing 15")
Even narrower gauge track

Scale: ~1:20th
Gauge: 9mm (representing 7")
Gauge 1 in the garden. Large scale, large space

See in particular the article on baseboard construction and the gallery for the photos.
There's a subtle difference between British "Gauge 1", which is a scale of 10mm to the foot (1:30.5 scale), and International "Gauge 1" which is a scale of 1:32. There's a detailed explanation here.
(N.B. (2024) these links don't work any longer. here were the baseboard pictures)
Scale: ~1:30.5
Gauge: 1¾inch, 44.45mm (representing 4'8¼")
Common name: Gauge 1