The British Library holds 351 of the original preliminary drawings made by the surveyors between the 1780s and 1840. They cover most of England south of a line between Liverpool and Hull. These drawings were produced as the base for the production of a one inch map for the country. Nowadays, OSD are value for genealogists for their place-names and by transport historians for their depiction of the expanding canal and turnpike road networks. They are seen as a unique record of land use in the eighteenth and early nineteenth centuries.