Smallest practical N-Scale layout(s)?

[railohio]

I guess it depends on what you expect to get out of a layout. You can build a 6" radius loop on a 14" square layout and run a trolley in a circle for hours. It runs, so it's a layout, right?

2x4' is about the smallest practical loop layout without severe equipment restrictions. I have a loop layout that's 18x34", but it's restricted to small switchers and 40' or smaller cars.