I'm totally new to model railroading. I am setting up a "N" scale set which will have many different diameters of track. What I need to know is, how is the diameter measured? I mean is it from the center of the track, or the outer parimeter? Let's say I have a 19" circle, is this measured in the center of the track, or the outside? From the center, it will be much wider than 19" from the outside measurement. I need to know this because I'm making a mountain landscape for this set for Christmas and this set won't arrive until almost Christmas. I want it to be a surprise.

Thanks

Don