problem with map blitting

I am working on an engine for my RPG in C++. I''m having some seriou problems with the algorithm for showing map that is bigger than the screen. I need to get it to work so the character can walk off the screen and the right screen will pop up. I have the data of the map stored in a double vector or whatever that''s called with map[height][width], so map[10][5] would be 5,10 (x,y).