A quick google-fu, which took less than 2 seconds yielded this hit where I got the information from, fyi - keywords without quotes "android gps offline maps"
Possibly two that might be of interest -
Navfree is a completely free navigation app that offers turn-by-turn
directions, spoken and on-screen instructions, offline map use and
address search and live search via Google and Microsoft Bing, among
many other features. The maps it uses are available for free download
from the Navfree Store. The map data is stored on your device so there
is no need for a constant data connection while driving. It also
allows you to browse maps anytime, anywhere without paying for data
connections, which means no costly roaming charges when abroad.
And the other -
MapDroyd features world-wide off-line maps powered by OpenStreetMap. Experience true unplugged vector maps avoiding expensive network connections.
Apparently, there's a way to do this - as documented over on XDA which enables you to create your offline maps for storage and to be used by the likes of Google Maps etc... Hope it helps! :)