SAN FRANCISCO  They don’t know it, but people who use Google’s online maps may be getting directions from Richard Hintz.

Mr. Hintz, a 62-year-old engineer who lives in Berkeley, Calif., has tweaked the locations of more than 200 business listings and points of interest in cities across the state, sliding an on-screen place marker down the block here, moving another one across the street there. Farther afield, he has mapped parts of Cambodia and Laos, where he likes to go on motorcycle trips.

Mr. Hintz said these acts of geo-volunteerism were motivated in part by self-interest: he wants to know where he’s going. But “it has this added attraction that it helps others,” he said.

Mr. Hintz is a foot soldier in an army of volunteer cartographers who are logging every detail of neighborhoods near and far into online atlases. From Petaluma to Peshawar, these amateurs are arming themselves with GPS devices and easy-to-use software to create digital maps where none were available before, or fixing mistakes and adding information to existing ones.