Add to that a purpose and back-history for your route.
What's the purpose?
- Is this a tourist line?
- Is this a mainline Class I railroad with many feeder lines, branches, and connecting railroads?
- What industries does the rail line serve?
- What towns?
- What other railroad interchanges with the railroad you're building?
The back-history.
The purpose of a back-history is to keep the scope within reason for the route. Before I built my current personal route back in early January 2004 after experimenting in December 2003 with route building, I based my route on local history and geography in my area. I have an extensive route history which I have written down and updated periodically. This story reads like one of those chapters in the Kalmbach Shortline and Operations books with history on local short line railroads. This back-history has kept my choice of assets within the geographic area to what they would be if this was the real world. I chose certain buildings and trees and the kinds of industries, and when setting up sessions over the years, I have kept the trains to the kind found in my area that I built. This background for the route also prevents things such as coalmines in the Grand Canyon and other things that don't make sense, and really does make finding assets a lot easier.
As for starting a route, I recommend looking at lots of pictures of real railroads in the geographic area you are interested in including maps as well. Google Earth, Topographic Maps, Historic Aerials, and many other maps services located worldwide, are your friend. These various maps will give you an idea on how the yards and terminals are laid out, and the pictures will give you a picture, no pun intended, on what the service looks like, or looked like in the past.
Start really small. My first route started out as 4 baseboards. Yes, A little cube in the middle and grew up from there as I expanded the route. My route is now 18 years old this year and covers about 200 miles of track counting branches and yards. I didn't work on it every day and I didn't work on the huge map all at once. It festered, grew, morphed, things changed, got deleted, the route shrank, and got rebuilt over time.
Plan on throwing away your first attempts. These can be considered as experiments in your building methods.
Look at what others have done. Open up one of Jointed Rail's routes if you have any. Download some of the great masterpieces from the DLS and open them up. Learn what these guys did and use their techniques in your own style.
Plan on stepping away and doing other things because creative processes will melt your mind and turn your brain to mush. You need to see the forest instead of just the trees.
Once you build a big part, drive it and enjoy the fruits of your hard-earned labor. This drive around is not only rewarding but it's also a way to see things that need a bit of fixing such as floating trees, branches in the way, walls and buildings not seated, and bumps and lumps in your track.