At over four thousand square miles, Salar de Uyuni is the world’s largest salt flat. The Salar is covered by a few meters of salt crust which has an extraordinary flatness, the average altitude varying by no more than a metre over the entire area: the expanse, clear skies and exceptional flatness make the Salar an ideal place for calibrating the altimeters of Earth observation satellites. The early morning and evening sun embosses the drying salt formations against the purple and pale blue skies, but for most of the day the brilliant light and whiteness of the salt eliminate any sense of shape, distance or texture, and the sun can cause blindness if proper protection is not worn.