tilemaps in 2d games

tilemaps in 2d games

I have 160 'world tiles', each world tile has 25 region tiles, each region
tile is 100x100 grid 50px by 50px
what do i need to know to be able to make it such that:
1). Initial zoom is the region tile. (100x100) 2). When player 'explores'
onto another region tile, the 2nd region tile is added to the player view;
and the player is now able to zoom in and out to show all explored.. down
to initial region.
do I just create one large image and work with that?? I am confused and
been looking through a few java game programming books to find an answer
on how to approach this with no avail.