To clarify, only WiFi+Cellular models of iPad incorporate GPS capabilities; GPS functions are built-in to the Cellular chipset. While you require a WiFi+Cellular model, you do not need an active Cellular plan to use GPS functions.
By contrast, WiFi Only models of iPad have Cellular hardware at all - and therefore also lack GPS capabilities. While a WiFi Only iPad has no built-in GPS capability, you can use a third-party Bluetooth GPS receiver with your iPad to provide GNSS. BadElf and Garmin Glo are two examples.