You can buy map packs through the online shop.
You can even impor some Ozzie Explorer maps.
My preference though is to calibrate my own.
Cuppa, check out my how to mate, it shows how to import and calibrate maps. Tou can also download the free PC app that let's you set tracks and waypoints etc in the PC which is a bit easier than doing it in the app.
For those that don't know, the Hema app is the same as Memory Map just with the Hema maps bundled.