Does anyone know if using GPS heavily affects your data use?
Well you need to define what you mean by "GPS" first.
If you mean opening Google Maps and simply locating your device precisely, no that hardly uses any noticeable amount of data.
If you mean loading large maps in new areas, that'll start using data, in the 10's of MB's at most if it's caching an area of tens of square miles.
If you mean loading and using Google Navigation for turn-by-turn navigation, it'll use the same amount of data. It has to both load the maps and load the driving directions. Still, hardly any amount of data.
Also Im gonna assume that the GPS has nothign at all to do with the network that you are on. Just wanna confirm this.
What do you mean by this? Do you mean which carrier you're on? Or which data type (2g/3g/WiFi)?
As far as carrier, no, not really. CDMA phones (Verizon, Sprint) often use network triangulation to supplement actual hard GPS fixes, whereas GSM phones are more likely to rely on the actual GPS chip.
As far as network type, that doesn't really matter either. Whether you're on EDGE, 3G, HSPA+ or WiFi, the GPS will load the same with assistance from the network. The only thing that will change is the time it takes to locate you. On a slow connection, if you don't have a good view of the sky for the GPS chip itself to pick up satellites for the location, it'll rely on the network more and it'll take longer if you have a slow connection.