I don't have an apple product, but have read about Viewranger, which is a a free GPS mapping app that works on both.

http://www.viewranger.com/en-gb

Allows downloading of openstreetmap maps and online/offline route planning.

I'm currently researching replacements for my laptop based photo and GPS trail management while on the road with an android tablet and came across viewranger and it sounds very promising for the GPS side of things.

You can also buy "tiles" (100sqm) of OSM maps at 10p a tile.