Texture Atlas
From TrainzOnline
We have learned that sharing materials is a good thing, but often one mesh object will require a completely different set of textures to another mesh object (e.g. you won't share Asset 1’s brick texture on Asset 2’s car model).
Instead, what we do with assets that are regularly going to appear in the same scene, is to combine several textures into one and remap the UVs of the meshes to look correct using that new combined texture.
A "texture atlas" is just a fancy name for this technique of packing a number of textures into one larger texture.
This example shows what happens when we combine two individual 1024x1024 textures into one 1024x2048 texture.
