The mobile location tracking app uses GPS and Google APIs to deliver pinpoint accuracy on your field personnel location. So, every activity on location is geo-tagged. You know when he reached, the time he finished and left for the next location. Even the photos taken on-site have a location tag.
Each service ticket that is pushed to his field service management mobile location tracking app has a site location and that is geo-tagged as well. So, all he has to do is point to the site and navigate using Google Maps on his mobile.
Maintain history of activities tagged by location and flag outlying behavior.