You could use a custom user field and a user group promotion into Town A, B... automatically based on that. However, you'll need to pre-populate all the towns if you do this. This might not be an issue if it's 10 or so towns, but it'd get pretty work intense if 100s and you don't build an add on to import them as custom user fields based on a CSV (or text file, etc.) to create each group and promotion for them as well.