Migratory birds and military aircraft—like during World War II—often fly in a V-shaped formation. The “V” formation greatly boosts the efficiency and range of flying birds, because all except the first fly in the upward motion of air–called upwash–from the wingtip vortices of the bird ahead.
In this image of a dune field in a large crater near Mawrth Vallis, some of the dunes appear to be in formation . For dune fields, the spacing of individual dunes is a function of sand supply, wind speed, and topography.
Written by: Alfred McEwen (audio: Tre Gibbs) (12 February 2014)
More info and image formats at http://hirise.lpl.arizona.edu/ESP_034815_2035
Image: NASA/JPL/University of Arizona