Not every iPad has got a GPS system. To be able to use the navigation on your iPad, you need a "Wi‑Fi + Cellular Model". If you are not sure if your iPad is such a device: only these devices enable you to use SIM cards. If your iPad does not have a SIM card slot, it does not have a GPS device.
Google Maps also uses the WIFI network and radio masts, so you might be able to use that in the city as well - we only use the GPS system however.