[inquisitor]

The smaller the billing increment, the cheaper for you and 1KB is the smallest billing increment available in the market. Here in Germany billing increments are at least 10KB, allthough the larger billing increment is offset by the way lower data rates here.

While downloading ephemeris for GPS (AGPS) generates only a few dozen kilobytes, Google Maps is way more data-hungry. Just opening Google Maps and viewing the map extract at your current position will download at least 100KB. If you then start panning the map, searching points of interest and calculating routes, you can quickly generate several hundred kilobytes within a minute.
In order to save data volume you should not use satellite view, as the satellite images are larger than the plain map view images, but in any case Google Maps can draw your credit quickly and is not suited for permanent use at French data rates.
In the beginning better check your credit after each usage of Google Maps in order to get a feeling on how expensive it is.