Nether fast-travel:
The nether is, coordinate wise, an exact match with the real world at 0,0. However, there is a 16:1 ratio size-wise for the nether vs the real world. This is only applicable to the X and Z planes, the Y plane is 1:1.
This means if you create a portal at 0,0 and another at 1600,1600 in the real world, those portals would be at 0,0 and 100,100 in the nether. This means you can traverse huge distances by creating two portals, and finding them in the nether. It is HIGHLY recommended to construct a road/rail/tunnel between them, and build it out of cobble/stone/obsidian and/or glass. Weaker substances are decimated by explosions, and although we've yet to encounter one, Ghast fireballs will trash netherack.