The Ordnance Survey Great Britain County Series maps were produced from the 1840s to the 1890s by the Ordnance Survey, with revisions published until the 1940s. The series mapped the counties of Great Britain at both a six inch and twenty-five inch scale with accompanying acreage and land use information. Following the introduction of the Ordnance Survey National Grid in the 1930s the County Series maps were replaced by a new series of maps at each scale.