Google has 35k engineers, out of which maybe 2-3k work on Maps. The 10k number probably refers to total number of workers (mostly contractors) that contribute to Maps: Street View, testing, imagery, notation, etc.
Google has 38,739 employees. 90% of them are engineers? No way. When I was there, MTV campus was like 35% engineering.
From Google Q1 2013 earnings report:
"Headcount – On a worldwide basis, we employed 53,891 full-time employees (38,739 in Google and 9,982 in Motorola Mobile and 5,170 in Motorola Home) as of March 31, 2013"