Setting Map Borders
After you've determined the edges of your transit system, you'll need to establish a set of definitive borders for your game's map. As we've mentioned, the scale of your map is entirely up to you–whether it spans your country or continent–but it is crucial that all players are using the exact same set of borders. In some cases, these borders can be naturally emergent and easily standardized; a game that spans a single country, for example, can simply be contained to the borders of that country. For smaller scale games–like those that take place in a single city or metro area–natural borders might be more ill-defined. (How big is Atlanta? No one knows!) In these cases, we would recommend setting your own hard borders using a tool like Google My Maps. Generally, it's best to draw a square or circle that encompasses the totality of the transit system you plan on using for your game.
It's also extremely important to ensure all players feel safe going to all areas of the map. Players should discuss safety beforehand, and if there are any areas where players would not feel comfortable going, they should be excluded from the map.