N Scale model railways are the world’s second most popular scale. They actual scale is 1:148 or 1:160 (depending on what part of the world you obtain models from), but they all run on tracks that are 9mm wide.
The other popular scale for model railways is HO. This scale is 1:87, with tracks 16.5mm wide, so the models are nearly twice the size as N Scale.
This means that it is possible to get more N Scale model railway into any given space than HO Scale.