In reply to rodw:
We bought the whole of IGN France at 1:25,000 via memory map and just put on on micro-sd card on phones.
Not cheap, £150, but can use on 5 devices (phones, tablet & PC), and then never without it.
Have done the same with OS for UK at 1.25.000.
Use in in combo with Google maps & OpernStMap.
Post edited at 22:29