I should add that the scale is 1:1, therefore a route which is 156 miles long in reality is the same in the sim. Ditto, scenery objects, railway/railroad objects are scaled 1:1, although there are exceptions, where the track gauge is not available and scaling up may be required. We do this for 3ft 6in gauge, which is not catered for, but 3ft gauge is and therefore modelled 1:1 scale.
We tend to use scale drawings from publications about real railways, and also scale drawings for model railways, too. However, lack of a plan has never overly bothered me and I've built locos from photo references only. There's only one way to skin a goose.
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