Sand seas and dune fields are important depositional landforms in many mid- and low-latitude deserts. Most sand seas and dune fields exhibit clear spatial patterns of dune morphological type as well as variations in sediment thickness, dune size, crest length, number of pattern defects, and spacing. These patterns reflect the self-organizing nature of dune systems as well as the external geomorphic and climatic boundary conditions - such as wind regime, sediment supply - in which the sand sea has evolved.