IPhones have GPS
3G model ipads regardless of size or memory have gps
wifi only have no gps
to run a wifi only ipad you need a bluetooth external gps eg Dual 150 or 160.... I have the 150 and it works great... The 160 came out and had some bad reciews initially, not sure if firmware updates have fixed it...
The big advantage of getting the dual over a 3 g ipad is that you can then buy secondary or repoacemeent decices, take friends, loan it, etc and convert anymes device to gps...also you can buy a very cheap aldi tablet or similar for under 100 and use it as a backup device...
The big advantage of the 3 g model is you dont have to hotspot data from the phone, thus you can save some phone batttery , just in case.... Also when not flyng you have a 3 g tablet... But i domt go anywhere without my phone anyway...
The cost of the sim and data for the tablet is pretty expensive, given once your maps are downloaded at home or on free, land based wifi, you really dont need much data... When i was running data in my previous ipad i purchased the Telstra 12 GB and only used 2 GB in a year... Mainly because im always near wifi...and when im flying it hardly uses any data.... dad who is not as data heavy as I, but also not as data cluey or savy uses about 1 GB and then does something silly like downloading maps or doing updates while on 3g .... So in reality you dont need much data at all ...and if you have data on your phone that can be hotspoted then you domt need any..
The only data you really need is your naips, then for ozrunways or avplan to grab the CTA and weather updates...
These are tiny amounts of data if done in the apps... Its the map updates that use all the data...and you can avoid mishaps there by simply launching your ipad at home into avplan or ozrunways and it will run the updateds on wifi ...
After having data on my ipad and now none, i find it far more convienient and far better value to have all the data i want or need on a hotspot capable mobile... That way my phone is like carryng a computer and i dont have to lug my ipad around to take advantage of the unused data on it...
The other option is buy the 3 g ipad which has the gps in it, leave the sim out and then just hotspot the data.. No external gps required.