Hi Roger.
Welcome to the forums.
There is Dem data availble for pretty much most of the globe now, although apparently the better quality Dem data is not free.
I use the free data available, but I use the Payware program TransDem to create the terrain in Trainz.
TransDem also allows you to create basemaps using maps or Google images, making it much easier to place things in their correct position, although there is as lot of work to be done with the images taken in Google Earth before they can be used in TransDem.
To give you an example, using Google Earth, you move to the area you want, at a height of 500m, place a google marker, save a screenshot, save the georeferenced marker file, load the screenshot into TransDem, load the marker file into TransDem, convert to UTM gird format, save new georeferenced files.(phew)
You do this for every screenshot you take in Google Earth, as you move along your route.
As you can imagine, each one takes a little while, and my route has now extended to around 1050 Google Earth screenshots!.
Although a lot of work, and it seems like you're not getting anywhere after a while, when you've done all this preparation work, you then find the correct Dem data and download it, load it into TransDem, overlay all your georeferenced images in TransDem, export the Trainz terrain, and then export the basemaps with map images at around 5 or 10 a time, and before you know it, you have everything you need to make a realistic version of the route, along with basemaps with the google images on, all placed on the route in the correct place showing you the rough area of where things go.
A lot of work, and I'm still working on Newport to Cardiff at the mo (laying track that is, all the TransDem work is done now, and the whole route is available to look at in Surveyor), but well worth it.
Mind you, it's not surprising I'm still working on the Newport to Cardiff trackwork, because as well as building the route, I'm also creating landmark 3D models for the route, and writing script Rules that I need that aren't available currently.
Take a look at the TransDem threads on the Auran forum for details on it.
It depends on the size of the route you're going to build, but there was no way I wanted to manually build the terrain from Cardiff to Cwmbran to Gloucester to Bristol, so it was a must for me.
Have fun,
Smiley.