Can I use my iPad mini as a sat nav?

All iPad models are available as either WiFi Only or WiFi+Cellular...

You need to understand that only WiFi+Cellular models of iPad have GNSS/GPS capabilities - 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 iPad 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. 

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 may 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, but ensures that you have immediate access to GPS/GNSS positioning services.

If using a WiFi Only model of iPad, you will need to provide GPS capabilities using an external GNSS/GPS receiver. These are often used in marine, aviation and vehicular applications - and can be either directly connected via Lightning or via Bluetooth. There are various third-party manufacturers, of which two are BadElf and Garmin GLO.

Also consider the software/App that you intend to use for navigation. Your iPad must be able to run the appropriate version of iOS/iPadOS for your chosen App.

For information, here is a list of the highest version of iOS supported by the older models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:

32-bit devices (obsolete)

iPad1 - iOS 5.1.1

iPad2, iPad3 and iPad mini1 - iOS 9.3.5 (WiFi Only models), iOS 9.3.6 (WiFi+Cellular)

iPad4 - iOS 10.3.3 (WiFi Only), iOS 10.3.4 (WiFi+Cellular)

64-bit devices

iPad Air1*, iPad mini2 and iPad mini3* - iOS 12.5.7

iPad Air2, iPad mini4 - iPadOS 15.8.3

iPad5, iPad Pro (9.7"/12.9" 1st generation)* - iPadOS 16.7.10

iPad6, iPad Pro (10.5"/12.9" 2nd generation) - iPadOS 17.7

(*) obsolete

Newer models are all able to be updated to the current version - iPadOS 18.0.1 (17.7 optional)

• iPad Pro 13" (M4)
• iPad Pro 12.9" (3rd generation and later)
• iPad Pro 11" (1st generation and later + M4)
• iPad Air (3rd generation and later + M2)
• iPad (7th generation and later)
• iPad mini (5th generation and later)

An iPad mini 4 (2015) would be the oldest one I would think would work for that.

Anything older, will likely be incapable of running any of the current navigation apps.

And yes, as mentioned, it will need to be the Wi-Fi+Cellular model.

https://www.apple.com/ipad/compare/?modelList=ipad-mini-4,ipad-mini-5th-gen,ipad-mini-6th-gen