Click layers, show zones, its in the bottom right of the screen.
It shows residential commercial and industrial areas, lighter colours are higher value which usually means high rise/ high pop structures so putting your Bus/ tram stops there in feeder to the stations gives people a faster route to your railway.
I usually just have a route going in a straight line through the most densely packed part of the city, turning around at the last stop and coming back down the line, this enables people coming to the city routes to work/ home and people going out of the city a route to the train station (or bus station if your using road vehicles to connect a few citys) make sure you bus lane the route as the traffic gets retarded, bring on the traffic lights.
