To use the maps while you are OFF-line, you can do the following:

Before your trip and while you are at your home with Internet connectivity, you can download all the maps of the places you will be visiting by defining "areas" (an area is a square defined by its upper left and lower right coordinates -latitude and longitude-) which will be saved to your memory in the NIT.

I follow the following procedure:

Everytime I travel I log into Google Earth in my Linux PC, I do find the coordinates of the area I want to have the maps and then go into my NIT, open Maemo mapper, on the menu go to :
Maps -> Manage maps
Then select the "Area" tab and define the top-left and bottom-right lat and long coordinates.
Now click on the "Zoom" tab and check the level of zoom in (detail) you want, level 0 being the closest to the ground).
Click the OK button.

Maemo mapper will then go to Google Maps (or whatever your selected map server is, like OpenStreet, VE Street, etc.) and download all the maps that correspond the the defined area with all the defined zoom levels you marked.

Bear in mind you many need a large memory card to store all the maps.

An advice: On the menu again: Maps -> Maps -> Manage Repositories it is recommended to change, per each map server (as indicated above), the Cache DB directory to point to your external memory card. As an example, for Google Maps I do have:

/media/mmc1/Maps/GStreet.db

Hope this information helps.

Kind regards.