Ok I need a little help here. I've decided on a new layout and am going to base it off of the Missouri, Kansas & Texas RR (KATY) and the Texas & Pacific RR. The era will be around the mid to late 30's. My main town is going to be Fort Worth, where I grew up, with the focal point being tower 55 where the two lines cross. I'll of coures have the stock yards in there, even though neither line serviced them, along with the T&P 360 degree roundhouse.

Good morning everyone,

After much time gathering, reading and digesting lots and lots of information (thanks to you all for pointing me in the right direction!), I have finally drafted another sketch (and hopefully better one) of what I'm planning to do, and yes, I took the whole year for that!!! 

The premise for the O Scale Traction Line is it serves industries in the city and heads out into the countryside to reach a lake where the trolley's take passengers/tourists to this popular vacation spot in the Spring and Summer. 

Unfortunately, with the reconfiguration we need to do to be in compliance with the fire code (a previously boarded up set of windows have been renovated and now have an emergency exit in them so we must have a 4' aisle with nothing in front of it at all times) part of this traction line must go into a tunnel. 

This question is about a design aspect I haven’t seen discussed much.

Question: to how much detail did you plan the location of scenic features (ie, rivers, canyons, etc) and structure placement before starting to cut roadbed for a mainline?