It's rare. Very rare even to be emphasized. The modder davidtime (probably French moreover) made a complete map for Bus Simulator 18. Available for free download on the Steam workshop, Greville, that's his name, gives us a little change of air.
Of the 700 mods available on the Bus Simulator 18 workshop, only 6 are maps. This shows how complex it can be to produce external content on this simulation. Most are bus reskins. And since Valve's platform is free, you can find anything and everything. That is not the case here.
The Greville map seems to be strongly inspired by the region of Grenoble with districts and points of interest called "Romanche" or "Saint Martin du Néron". Google Maps is our friend to find the consistency of these places. Technically, if we are not at the level of finish of the original map of the game, Greville defends itself well and especially makes us change air. Because it's been more than 2 years that we travel Seaside Valley and we end up driving with our eyes closed.
Greville weighs a little over 1 GB on the scale. You will need to start a game from zero and select it. It has its own weather system with thunderstorms that shake the office if you are equipped with a subwoofer. Despite all the care taken by Davidtime, we have encountered game crashes at times, for no real reason. Maybe you will have better luck. To install it, MEET HERE, and click on "Subscribe". The map will load in your installation.