The TransMat is housed in a Ziggurat in the center of the main cities.
The Ziggurat is also the official government building. Streets radiate from it.
Where you able to look at the city from above it would look like a giant ziggurat itself.
There is transportation stations outside the Ziggurat that will allow you to access the city or go to another city. In Terran the transportation vehicles would be referred to as Taxis and trains.
Trains take people to other cities on the planet. For Natives there is no fee, but for tourists there is a nominal fee that allows access to the trains for the entirety of the stay.
Taxis are for transportation within the city. There are fees.