So, first of all you need to use an asm routine!
The original main routine it located at 080A2F54, while the one that loads the name of the city is at 080A30E0.
In my case, I attached my routine to 080A3102, like this: 0000480047xxxxxx08.
After, i created a table in which each entry is composed of [2 byte - bank map][4 byte offset image][4 byte offset palette].
All you need to do is scroll the table and look for the map entry where you are currently!