On a snowy morning in early March, looking for the frontiers of digital mapmaking, I hopped into the back seat of an SUV sporting a Global Positioning System receiver on the roof. In front sat two representatives from Navteq, one of the companies that builds the street maps that you see on MapQuest. Phil Satlof, senior geographic analyst, operated a laptop computer hooked up to the GPS receiver.

Looking at the computer's screen, I felt we'd stepped inside a video game. A flashing arrow showed our progress through the familiar grid of Washington's streets. I watched, fascinated, as it marched down a line marked "River Road" into Montgomery County, Maryland.