Survey flights: aircraft flying parallel lines

Aerial photography, mapping and geophysical survey flights often cover an area in long, straight, evenly spaced lines, turning at each end to fly back alongside the previous line. On a flight-tracking map the result looks like a mowed lawn and is one of the easiest flight patterns to recognize. Lidar mapping flights overlap the strips they scan, and the USGS specification treats an unscanned gap between strips as grounds for rejecting a project. A 2018 USGS magnetic survey of Michigan's central Upper Peninsula flew lines about 500 ft apart and 260 ft above the ground, closer than the spacing this site looks for.

The site looks for at least six alternating straight legs, each at least 3 nautical miles long and within 10 degrees of a common axis, flown over at least 30 minutes. Successive lines must step consistently to one side by 0.2 to 2 nautical miles, and the altitude must stay within a 300 ft band. Shorter sets of back-and-forth passes are recorded as parallel passes, which add context to other stories and do not get stories of their own.

The shape matches survey work, but training flights, searches and patrols can fly similar lines, and the data does not say which one it was. The track also shows only the part of the flight these records captured, so a survey can extend well beyond the lines drawn on the map, and a gap in the data can make two lines look like one.