The first geological map of London was published in 1856 by Robert William Mylne, son of William Chadwell Mylne, 'Engineer to the New River Company' which supplied London with fresh drinking water from the River Lee in east London.This map was published in a period of great change in the understanding of public health and disease in cities, and for the urgent need for improved water supplies and sewerage systems. A geological map was essential.The 1871 edition of Mylne's map has now been reproduced by the BGS as a faithful facsimile of an original held in the Survey's library. It offers a glimpse into the history of urban development in London in the mid 19th Century - a wonderful map for any London historian.