| Reference text: |
US Department of the Interior, US Geological Survey (USGS), National Mapping Division. Standards for 1:24,000-Scale Digital Line Graphs and Quadrangle Maps, Part 7: Hypsography [online]. Denver: USGS, 2001 [cited 13 November 2003]. Available from World Wide Web: <http://nationalmap.gov/standards/pdf/7dqm0401.pdf>. |
