Yes it does, the maps are not actually stored on your iPhone but are streamed to your iPhone during use. To cut down on your data usage, you may want to download one of the many GPS navigation apps that allows you to download maps for offline use. I use Navigon, myself. It's not cheap, almost $50.00, which includes a full North America map set. To save on storage space, you can only download those maps you will need for your trip.
If you need something while you are tooling around in town, you can use CityMaps2Go. It will let you download cities needed and then your gps will work within that location. I used it in Italy and worked like a charm.
Of course it does, specially if you are with a Internet connection through 3G or LTE or anything, the localization and the loading of Maps consumes a lot of data