I used an OSM-based map on my Garmin on trips to India; did five trips to Bangalore and often played tourists on weekends; I had a particular interest in the ancient temples of Karnataka. I used a driver who knew the sites well, but not always perfectly, and the map was a huge help; coverage of roads in rural areas was quite good, not perfect but several times got us around closed roads the driver was familiar with and onto good alternate routes.

Not sure how much of the mapping was done from aerial imagery and how much was actual GPS tracking, but it was better than I expected. And this was about 5 years ago.