I found that I could not accurately survey my land. Or perhaps it was just too much effort? Either way, it’s not like laying track in a basement where all you have to deal with are uneven floors and non-right angle walls. It was almost impossible for me to accurately locate the exact shape and size of every tree trunk, bush, or root.
Sure, I measured the yard to get the basic dimensions so I could see what might be possible and draw a basic track plan, but it certainly wasn’t at the level of accuracy needed for a detailed plan. I even got a digital level that reads out in %.
But, I did better when I took some track outside and started laying it in the place I thought I wanted it. Often, I would encounter a root or some other obstacle and have to change my plans. Once it was lying on the ground, I just used some big rubber bands to make sure the track pieces would stay together; then, I would run a train and see how it looked, or if it struggled on a grade. Pulled around the # of cars I wanted to run in both directions. Then I used some bricks to elevate the track where needed until the grade was where I wanted it to be. That’s how I discovered where I needed bridges or long trestles.
My basic plan did not survive contact with the yard, especially when I would discover a giant rock (BFR?) or a hidden root while doing some digging. Changes were made as I put down track; sometimes just because I thought it would look better than my original track plan if I went wide around a bush, instead of curving in front of it.
Remember, there’s no race. Take your time.