John Rocque's maps of London were published in 1746. A French-born British surveyor and cartographer, John Rocque produced two maps of London and the surrounding area. The better known of these, depicted here, is a 24-sheet map of the City of London and the surrounding area, surveyed by Rocque and engraved by John Pine and titled A Plan of the Cities of London and Westminster, and Borough of Southwark. Rocque combined two surveying techniques: he made a ground-level survey with a compass and a physical metal chain – the unit of length also being the chain. Compass bearings were taken of the lines measured. He also created a triangulation network over the entire area to be covered by taking readings from church towers and similar high places using a theodolite made by Jonathan Sisson (the inventor of the telescopic-sighted theodolite) to measure the observed angle between two other prominent locations. The process was repeated from point to point. This image depicts all 24 sheets of Rocque's map.Map credit: John Rocque and John Pine