I started with a plan drawn with compass and straightedge on paper, and worked it up electronically using the Atlas Right Track software, just to see how far that would take me. I wanted two main lines, with the inner one having a yard lead, servicing a roomy yard including a runaround and access to a turntable.
I then made a mockup of the basic topology using a bunch of old brass Atlas track I had, pinned down to a 6×10-ft (185×305-cm) slab of foam, built up from 1-inch (about 2.5-cm) sheets. These overall dimensions were constrained by my maximum reach across the table (being 6-ft tall this is just barely 3 ft) and the length of a room that might house it. I've been told that a 3-ft reach is too much to impose, and ordinarily I might agree. But since this layout can be lowered completely to the floor, the extended reach is possible.
I added a reversing loop around the yard which I later removed. This composite foam board is a sandwich of three 1-inch-thick layers, each made to interlock to make the assembly as strong as possible (and because they are available only in 4×8-ft (122×244-cm) sheets.) The 6×10-ft slab of foam is surprisingly rigid and light. I made the mistake of using hot glue for the assembly. In retrospect, a much better choice would be specialized foamboard adhesive, such as that made by Liquid Nails.
Satisfied with the operations of this topology, I transferred the basic idea to a drawing of the layout, since Right Track is as limited as the sectional track it is intended to sell.
I made a good scale drawing, experimenting with curves of various radii, and transitions, and such. The drawing I then transferred to the foam board, set up on sawhorses in the garage.
Here's where I got to experiment with the yard layout. I wanted a ladder yard, with a runaround, a siding to stash the yard engine, and a track into the yet-to-be-sited turntable. There is a definite tradeoff between the number of tracks in the yard, the size of the turnouts, and the usable length of the resulting yard tracks. At this point, I wished that I had made the layout a couple of feet longer, at 6×12 ft. I settled on #6 turnouts for the entrance into the yard and for the first few yard tracks in order to accommodate the long passenger cars and other long rolling stock. The rest of the yard had to use #4 turnouts, due the severe space constraints. In the end, this has not presented operational problems.
In the foreground of the following picture you can see the only pieces of track that are not Shinohara: the three Atlas code-83 rerailers, which required moderate thinning by sanding to make them the same height as the other track.
This evolved into the plan below, which is the as-built layout. The yard tracks are not as long as I would like, but the effect of the ladder yard is there. If this were a 6×12-ft layout, all the yard tracks could be extended by 2 ft, which would be really nice.
After adding some of the details, it looks like this:
A natural place to go from here is to the benchwork section or the track section, depending on your interests. These next aspects of the layout develoment sort of co-evolved. I had to build the foam base first, then layout the track design, so that I would know how to build the benchwork. I needed to make sure that none of the benchwork got in the way of the many switch machines that would require mounting from underneath. That's covered in turnouts.