My first test of an on-line map was asking for directions to the house of my business partner. Mapquest had me turn off a street running along the bottom of a cliff onto one that ended at the top of that cliff. From an airplane, or to a computer that took into account only the N-S and E-W coordinates of a point, they probably look like they intersect, but it's hard to drive up the cliff.

Fortunately, I had been there several times before and knew enough to go the long way around to the other end of the street at the top of the cliff, but if I hadn't ...