On every diagram in 101 Track Plans, Linn Westcott drew a grid of evenly-spaced lines, accompanied every few pages by a legend like this:
Ruled lines across plan are:
6" apart in N
9" apart in TT
12" apart in HO
18" apart in S
24" apart in O
If you have a plan and a modelling scale in mind, you can measure distances or find the total size of the layout by counting grid lines. The grid is what relates the picture to real-world measurements.
When you load a diagram into TrackLayer, the program just sees an array of dots. It doesn't know where the ruled lines are, or whether the picture represents a four-by-eight table, a fifty-foot clubroom, or a map of the county. You have to tell it. The first step in creating a layout is adjusting the TrackLayer grid to establish the dimensions of the image.
The grid is not normally visible -- you can toggle it on and off using View Grid -- but it comes on automatically when you load an image file. It comes up in an arbitrary position (as shown at left), and normally all you have to do is drag so the two grids line up.
Sometimes it's a little trickier. The legend for Springfield Electric Lines(plan #70) says the ruled lines are double-spaced -- 12" for N, 24" for HO, etc. -- in which case the TrackLayer grid has to be made twice as dense, as shown below.
For the complete list of the modelling scales and grid
separations built into TrackLayer, see
About Sizes and Scales.
You can do some interesting experiments with the grid. For example, suppose you wanted to build the Gorre & Daphetid (plan #17) in half the space. Double the grid spacing, and here's what it would look like:
Good luck navigating those curves!