In remote sensing, ground sample distance (GSD) in a digital photo (such as an orthophoto) of the ground from air or space is the distance between pixel centers measured on the ground. For example, in an image with a one-meter GSD, adjacent pixels image locations are 1 meter apart on the ground. GSD is a measure of one limitation to image resolution, that is, the limitation due to sampling.
GSD is also referred to as ground-projected sample interval (GSI) or ground-projected instantaneous field of view (GIFOV).
References
Ground sample distance Wikipedia(Text) CC BY-SA