Serving a 100 car siding is a little different than serving 1-2 car sidings in an industrial district, though--in my neck of the woods, local switching is done by older Geeps and MP-15s, although occasionally I see older SDs on the local turn.
Not sure how helpful it will be, but here is a shot of my switching layout...if you eliminate the switch that leads to an L-shaped protrusion the whole thing fits on a 1x6 foot table. I wouldn't try using this plan with modern full-sized units, but with something the size of a Geep or MP-15 it works just fine (I use Athearn GP-7 and SW-7 for switching when not running my 44-tonners.)
The basic idea for a six-foot HO switching layout is a runaround track/mainline portion and a couple of spurs to spot cars. In the photo above, you can see the runaround in the middle, a pair of spurs (one on either side of the mainline) in the foreground, each of which holds two cars, and a small three-track yard in the background (capacity 7 cars.)
The runaround track is there so you can spot facing or trailing point spurs, and makes things much more flexible. A couple of spurs gives your trains a reason to stop, and the yard, while too small to represent a big division point, is enough room to shuffle cars and also represents another "industry" destination that can receive any sort of car.
About DCC: While DCC is nice, it hardly seems necessary on a six-foot switching layout which probably won't have room for more than one locomotive. I mean, it can't hurt, especially if you plan to later expand this switcher into a full-sized layout, but it won't really help for that incarnation of the layout.
About the sample track plan provided: I am generally unimpressed by a lot of the Thor Trains plans--they don't really seem that logical. Trains are there for a reason, they do useful work, and it's more fun if our model trains can pretend to do useful work too. Aside from the no-runaround problem, there is no room on that layout for the industries that this railroad supposedly serves, and the layout of track doesn't really make sense for a yard. It just seems like an exercise in how difficult one can make it to move cars from one end of the switching layout to the other.
This kind of layout is called a "switching puzzle," and there are lots of reasons not to build a switching puzzle layout that I won't go into. Instead, I'll tell you the good things about building a shelf layout that ISN'T a switching puzzle!
My layout was built with the following givens: I like operation, I like urban railroading in cramped quarters, I like city scenery, and I don't care much about running trains around in a circle. My layout is small, and while I certainly could have filled every square inch with track I also wanted room for industries and buildings. You can't see them in this photo but there are actually two other industrial buildings on that layout, and another spur off to one side for a building I haven't built yet.
Same layout, different camera location. The stairs in the foreground are for the loading dock where the reefers are parked in the above shot.
Overhead shot, showing the things I haven't done yet...
Now, I'm probably spending more time on my layout that is really necessary, but the point is this. The module is only six feet long (although there is a second yard module that can attach to it, and eventually it will be part of an around-the-room layout) but it accomplishes the following goals:
It is not a puzzle. Every point on the layout is easily accessible to a switcher. Aside from maybe having to move a car out of the way of the "Cal-Hi Beverages" warehouse, no unnecessary car-shuffling--and that sort of respotting is prototypical.
It can be operated like the prototype to do Useful Work: trains come in under the bridge from a yard or a removable cassette, switch out old cars for new, and proceed down the mainline or back to the yard. I'm not just shuffling random cars for fun--unless I'm just in a mood to do that...
It has scenery. While it is not complete (I still need to do a backdrop, add a few more structures, add trees, and the bridge) I wanted enough room for industries, buildings, trees, homes, street details like stop signs and fireplugs, and those wonderful piles of railyard junk. The buildings that should be there as a reason for the railroad to stop by and drop off cars are present. While flats are an acceptabe option for an industry, you can only use flats against the back edge of a layout! "Off-screen" industries on the foreground edge are also possible, but you can't really model 'em and so it's somehow unsatisfying....
And finally, it's fun to run! It's not a frustrating puzzle, but trying to shuffle a bunch of cars in and out can result in some serious head-scratchum.
