This is a wonderful extension to the game. It not only adds details such as names for streets, parks, bridges, etc, but also adds tons of flavourful details about the geography and architecture of the city. There are tons of new river channels and bridges, overpasses, or gangways between houses, all of which add character to the individual districts. Details such as these can actively shape your gameplay, we even used the map not only for general orientation and roleplaying, but also as something akin to a battlemap.
For me, this is an absolute must-buy for game, and especially for this price I can absolutely recommend it!