Layers Quickstart Guide By Wreeder
Here is what I have discovered about layers. As long time users of Trainz are aware that in the past when you saved in surveyor certain items were saved with the route file and certain other items were saved with the session file. For example the track, groundtextures, trees and other scenery objects were saved with the route as were triggers and trackmarks. Rolling stock, edit session parameters, driver commands and interactive industry settings were saved with the session file. This knowledge was often the hardest for new users to understand and grasp.
With TS2010 and layers, this has been totally changed to what is placed on a route layer is saved with the route and what is placed on a session layer is saved with the session. There is something very different that you must wrap your head around to understand how layers can be used. That is that the only items required to be on a route layer are groundtextures and the baseboards. Everything else that has always been on the route can now be placed on a session layer. So you could create a new route in surveyor and go to the layers panel to make sure that the route layer is lighter than the session layer since the current layer you are working on is always lighter. Then you can make changes to the terrain and add some groundtextures. Go back to the layer panel and click on the session layer so that it is lighter. Add some track, buildings, scenery, triggers and trackmarks. If you save your work and quit surveyor then open just the route you will see just the baseboard and the groundtextures. Opening the session will bring in everything else. Now this is just an example and I wouldn't recommend building a route this way but it does show the concept at the most extreme.
In truth you should continue to build routes much the way you have always done. Track and scenery go on a route layer but now you have a better way of doing it by using more than one route layer. You add a route layer by clicking the (+) button in the layers panel and then choosing if you want it to be a route layer or a session layer and giving it a name. Think of the process like this, one route layer for track work, one for buildings, one for trees, bushes and grasses. If you do this then you can lock the other route layers while you work to get the fence line next to the track just right and you won't accidentally move a track spline or that station you spent a lot of time getting located perfectly. You can make any layer invisible so you can better see what you are doing and then turn the visibility on before saving. You can also merge layers together once you are finished working with them. Objects can be copied from one layer to another using the copy and paste tools.
Now the big deal with session layers is that you can add trackmarks and triggers here instead of the route layer and save the session. This means that other users can create sessions for another user's route without having to change the route itself. Just make sure the session layer is active and place your trackmark the same way as always. It looks the same but will be saved with the session. The same goes for triggers. Before you place rolling stock make sure a session layer is active. If the route layer is active then the rolling stock will be saved with the route not the session. So you can see that being aware of which layer is active is very important.
If you start thinking outside the box you can do some very fun stuff. For example, you have a siding that once had a station. If you place the station on a session layer then it will appear when that session is run but not be part of the route otherwise. This opens the door for having a series of historical sessions where the changes that the real railway went through can be created with sessions all using the same base route. What you need to remember is that all route layers are saved with the route and all session layers are saved with the session file. This is true even if a layer is not visible. Invisible layers will not show in Driver. What would be extremely cool is if the visibility of a layer could be changed through scripting while a session is running.
The possibilities are endless. The best way to learn is to just play with the layer panel until it makes sense to you.