The majority of data contained within the road line feature class was derived from the roads layer of Digital Chart of the World, edition 1, July 1992. All schematic road connectors added in urbanized areas for network connectivity were given an 'exs' (Existence Category attribute) value of '55' (Unexamined/ Unsurveyed). Where possible, road features were designated as primary or secondary routes by comparison with Operational Navigation Charts (ONC) map sources.