You have to keep in mind how cities are built, and how the railroads intereact with them. In the old days, the railroads went right into towns whereas today they're on the outskirts. If this is an older city, then the station and yard will be surrounded by buildings, or at least will run through the area. In the western cities, the yards are more spread out, and not even close to the cities. The cities themselves have track along the edges because they have the room to do so. Up where I live in the Merrimack Valley, the railroads had downtown yards and lots of branches feeding the textile mills. There were tracks that ran through the industrial canyons in Lawrence along the North Canal. Cities too don't just end, but seem to fade into the surroundings. They start off with lots of suburban houses, cul-de-sacs, and condo developments which eventually give way to some industrial buildings and commercial areas. This eventually leads to the concentrated downtown that then spreads out again to the similar structure on the oposite sides. I hate to say it, but similar to a leaf pile if you've ever raked leaves before. In the older cities, there maybe large spreads of older homes located near the old mills. These were the homes for the workers that toiled away in the old mills. The owners lived outside of the city away from the pollution and noise. These could be mini-communities unto themelves like the Acre, Belvidere, Ayer's Village, Collinsville, etc. These are areas around Lowell and Haverhill MA; both once big industrial centers. Today the mills are empty, but the houses are still there. Belvidere is nothing but big mansions from the great heyday of the textile mills. The Acre is the opposite. You wouldn't, or as I should say, shouldn't walk in that area alone!
So this presents an issue for us. What do we include, or what do we not include. Gven the studders we are prone to in this program,. we have to compromise quite often to keep the program useable. In general I keep the area to about 3 baseboards, meaning the track, railyard, and other main railroad stuff is in the middle with room for landscaping on either side. I also put larger buildings where I want to block views. In one of my cities, I also put in some hills as though the rails were in the valley. This particular area is under my minimum at one baseboard width. With the hills, mills, and track centered, there's no way of knowing how shallow everything is.
For buildings I keep the more detailed ones nearest the tracks, and less detailed boxes with images on them for the distance. Using a lot of long-block buildings helps too because you can get a lot of buildings for nothing regarding frame rate hit. I noticed too that since I've swapped to Speed Treez and their relations, I have had less of a hit on the framerates due to the GPU-driven rendering versus CPU-driven. This makes a big difference because the CPU no longer has to fathom out geometry for flip board trees, and can concentrate on the buildings which are nothing more than cubes for the most part.
If you're going to include off the mainline areas of interest, you need to use angles and close buildings. You don't need to have a lot, but enough to hide the obvious gaps. For this you can use blocks of mills, warehouses, and other tight corners to move into. Avoid those spline warehouses and mills. They'll kill the performance, and honestly I never seem to get them to look right.
I would like to add too that in general splines are a killer, and sadly in cities they're a must. I avoid fences unless I really need them, and keep power lines, except telegraph lines to the minimum. Grass clumps are okay, but don't go crazy with them. In fact I've put them and taken them out. They look okay, but also can be a frame killer when used with the thickness that they should be. A clump here and there just doesn't cut it for the areas I model, so rather than deal with studders, I've removed the grass and used a lot of textures instead.
Anyway, I hope this helps.
John
...........but with horses, right!