I totally agree with everything said above. Personally, I tend to do the landscaping first, then lay the tracks, and do the landscaping adjustments as I go, then I go back and add scenery (houses, streets, signs, etc).
The one exception is the route I am currently working on (and this is definitely NOT an example to follow). I started by laying the tracks, all of it, for a route that's about 400km total, based on what I could find on Google Earth. So I know my tracks are in the right position. Next, I adjusted the height of all the tracks (because I didn't think of doing it in the first pass), and adjusting the ground below it. Needless to say, it is a long tedious way of doing it.
Then, I heard of TransDEM, which I have used in the past, on earlier versions of Trainz. So now, I'm debating if I should just continue the way I started, or start from scratch and do it all over again...
But either way, as said by previous posters, you might want to experiment a little, start on something small, and see what "feels right" to YOU. Is it making your landscaping first, then the tracks, then the scenery? Or any other way around, or a combination? Experimentation is the best way to know what works best for you.
realm174