Chad Richey spends 30 or 40 hours a week fixing Waze maps and teaching other map editors his techniques. It isn’t his full-time job. It isn’t a job at all. He does it all free.

“I get the eye rolls or muttering under the breath when I bring out the computer” at home from his wife, says Mr. Richey, a 40-year-old product manager from Longview, Texas. “I tell her look, I’m not out playing golf.”

Waze...