Expanding upon information already provided by IdrisSeabright...
Your proposed usage model is perhaps unclear. Unless you require real-time positioning data while travelling, you don't require GNSS/GPS at all. Mapping Apps will work just fine in absence of real-time positioning, but will not show real-time position while you are moving.
A WiFi+Cellular iPad includes GNSS/GPS positioning functions that are not present in WiFi Only models of iPad. While GNSS/GPS functionality is derived from the iPad's Cellular chipset, the GNSS/GPS function is entirely independent of Cellular. As such, you do not require an active cellular plan to derive precise positioning data.
By contrast, WiFi Only iPad models have no built-in GNSS/GPS positioning capabilities. However, you can add this capability by using a compatible external GPS receiver - such as Garmin Glo, BadElf or similar.
If you are using an online mapping service, you may require a cellular connection when you are away from an accessible WiFi network. However, some mapping Apps (e.g., Google Maps and Apple Maps) allow you to download maps for use while offline without a network connection:
Apple Maps
Download offline Maps on iPad – Apple Support
Google Maps
https://support.google.com/maps/answer/6291838?co=GENIE.Platform%3DiOS&hl=en
If your chosen mapping App does not have its own offline map-set, or has the ability to download maps, this is when a Cellular connection will be required to access online mapping while away from WiFi networks.