There are no catchment area's, so the game can't show them.Well, considering stations have no displayed catchment area, I can only guess how close the bus/tram stops have to be to each other. Another flaw of the game...
People and cargo will just take the fastest route to it's destination.
So even a house or industry 1km away, might be in the "catchment area" of your stop, while another house only 200m away, might not be in the "catchment area". It all depends on speed, starting point and destination.

In general:
Faster vehicles => stops should be further apart. This counts for everything (from horse carriages all the way to the high-speed trains)
Also, when you know how the game works, making money is easy (at least on the easy setting).
The game works like this:
PASSENGERS:
People live in a house (green). They go from their house to their work (blue), shopping (red) and leisure (yellow) buildings.
They always go back and forth from their house (f.e. no industrial -> commerce traffic)
If you click a person, you can see where he/she lives, works, shops and goes for leisure activities.
All these trips, need to be within 20 min.
The more area's can be reached from a certain area (within those 20 min), the higher the land value and the bigger the buildings that will appear there (bigger building => more people, shops, jobs or leisure).
Keep in mind that the 20 minutes is the total travel time. This time includes: walking to stations, waiting at stations and traveling on vehicles.
The frequency time that you see in the line manager, determines the waiting time at stations.
People can use multiple lines without problem as long as the total travel time will not exceed 20 min.
CARGO:
A towns industrial buildings (blue) demand goods. Those goods can be delivered by 3 buildings: refinery, steel mill and sawmill. (there are mods that add more factory types)
When a town that demands goods has one of these buildings within 20 min, it will check if there is raw material present withng 20 min. If the material is available, the materials will be transported to the factory, and the goods will be transported to the town.
Frequency is not very important for cargo.
You can see if a factory is using your line when you click it. (it will say line usage: yes or no)