Map Pilot for iOS automates the data collection process.
Each green box that gets drawn represents an image that is taken by the camera. The darker the green, the more times that area has been covered. Ideally, the camera should be able to see every point you want to include in the map at least 4 times.
By precisely controlling the flight pattern, flight speed and camera frame rate, it is possible to achieve perfect coverage and overlap. Plenty of overlap and nadir (straight down) images are the key components to collecting great data and making great maps.