With the original idea having a spot where you double back, and a desire to have map that didn't extend 300,000 pixels, I needed more than 1 dimension for the map design. The idea was supposed to be; Apartment to Street Level, Metro/Underground to Downtown, Downtown, Double Back to Mall, Mall to Power Plant, Power Plant to Basement and Tunnel, Tunnel to Research District, Factory to Lab to Game End.
So where you go down, you go down more than you go up, allowing for the horizontal space to be better used.