You don’t need a Cellular plan to use iPad for navigating - but you do require an appropriate model of iPad… or an external GPS receiver.
Only WiFi+Cellular models of iPad have built-in GPS - this being a function of the iPad Cellular chipset. WiFi Only models of iPad have no GPS capabilities with which iPad Location Services can derive location. This fundamental difference may significantly impact your ability to use mapping Apps - in particular if real-time positioning (e.g., a moving map) is required.
WiFi Only models can only “infer” their location from a database lookup of neighbouring WiFi networks for which the geographic location is known, or the geographic location of your public IP address. For static applications in urban locations, where the location of IP public IP addresses and WiFi networks are known, an “inferred” location can be relatively accurate. However, in rural locations, or when using a Cellular/Satellite/VPN connection, location accuracy of an inferred location [if it works at all] may be very inaccurate. Without an active network connection, a WiFi Only iPad cannot derive location at all.
This has significant implications for non-static mapping applications. If you need to have moving maps, or have future flexibility to do so, you’ll need to consider a WiFi+Cellular model of iPad. Choosing a cellular model does not commit you to adding a cellular service plan for the iPad (for location services, you don’t need a cellular plan at all) but ensures that you have immediate access to GNSS/GPS positioning services.
While a WiFi Only model of iPad doesn’t have internal GNSS/GPS hardware, you can use a third-party Bluetooth GPS receiver with these model of iPad to provide GNSS. BadElf and Garmin Glo are but two examples.
