Mapping Apps, such as Navionics, are critically dependent upon Location Services.
Insofar as you needing a WiFi+Cellular model iPad, GPS capabilities are integral to the iPad Cellular chipset - however, GPS functionality is independent of Cellular. Whilst you may need a Cellular model iPad, you do not need to enable Cellular service with any Cellular Carrier.
Unlike iPhone and WiFi+Cellular models of iPad, WiFi Only iPads do not have any GPS location capability with which to directly determine their location - and as such are completely reliant upon their network connection to infer an approximate location. This limitation has further implications in that mapping Apps installed on your iPad cannot estimate your location without a WiFi network connection; no “moving maps” when away from home!
For WiFi Only models, lacking GPS, an approximate geographic location is estimated from a “database lookup” of (a) your WiFi Network Name (SSID) or detected neighbouring WiFi networks - and (b) the “public” IP Address provided by your Internet Service Provider (ISP). If the mapped WiFi network name or IP Address are not available within the applicable databases, or if this information substantially differs between sources, then your approximate location may not be computed. This situation often occurs if you are in a remote/rural location where neighbouring WiFi networks are scarce - or if connecting over satellite or VPN connections.
Network IP Addresses and WiFi networks are frequently mapped in urban and cosmopolitan areas (including “crowd source” techniques) and as such approximation of your location from lookup against these databases can be provide relatively high accuracy. As population and network density diminishes, this mechanism becomes progressively less reliable.
WiFi Only models of iPad can be augmented with a third-party GPS receiver - linking to iPad using WiFi, Bluetooth or wired connection. In some applications (such as Marine or Aviation, where it may not be possible for the iPad to directly receive GPS signals), it may be necessary to use an external GPS with a WiFi+Cellular model of iPad.
I hope this insight and guidance assists your understanding of what you may (or may not) need when using Navigation software.
