🗺️The Historical Value of Keyhole Satellite Imagery: 1983 Satellite Map of Changzhi

Keyhole (KH) is the collective name for a family of US optical reconnaissance satellites flown during the Cold War. From the first KH-1 in 1960 through the KH-9 “Hexagon” of the 1970s and the KH-11 that followed, the series returned a huge volume of film to Earth over more than two decades, imaging millions of square kilometres of the planet's surface. In 1995 the US government declassified early Keyhole imagery, and in 2002 released part of the KH-9 archive, turning these “eyes of the Cold War” into a historical base map that researchers, planners and enthusiasts around the world can use.

Keyhole imagery is valuable for urban research because of its long time span, complete coverage and correctable geometry. In Changzhi, the 1983 scene resolves main roads, factory walls, rows of single-storey houses and farmland plots; overlay the same spot on a modern image and the advance of the urban edge, the loss of farmland, and shifts in the river and railway become immediately visible. Many features that have since disappeared — fragments of the old city wall, factory spur lines, the old airfield — survive in full only in images like these. For local gazetteers, heritage protection and the tracing of land tenure, Keyhole imagery is hard to avoid.