I also use Back Country Nav, works off OS 1:25K Multimap in the UK, costs one off £6.99 and you can download (on wifi at home or off your phone data allowance) the map areas you want to use in areas without data signal, then delete them afterwards or keep them depending on phone memory. Overlay routes downloaded off the internet, record your own routes etc etc. I’m not aware of a BCN database of routes you can ref, but you can download and overlay .gps routes from other internet sources (and most certainly other formats). They have a 3 week free trial if you want to try it out (or they did).