3.2.1 Great Britain
The Ordnance Survey (OS) produces maps at several large scales suitable for geological base maps. Particularly useful is the 1:10,000 series which, with the order 1:10,560 (6 inches to 1 mile) maps it is rapidly replacing, covers the whole of Britain. There is also the 1:25,000 ‘Pathfinder’ series. The wealth of detail on these series, such as hedges, fences, paths, even sheep pens, make the accurate location of geological observations simple except, perhaps, in open moorland, where it becomes only slightly more difficult. The contour interval on all these maps is 5 m (10 m in mountains). The 1:10,000 maps are sold as flat unfolded sheets covering 5 km x 5 km. Pathfinder maps have the same V.I. but cover 20 km x 10 km. They can bought as flat or folded sheets and ‘outline’ version is also published.
OS produces maps at still larger scales. Geologically, the most useful is the 1:2500 series, referred to as ‘25-inch’ (to the mile) maps; they cover all but larger urban areas, moorland and mountains. The OS will enlarge these sheets up to 1:1250, or even 1:500. Larger urban areas are served by their own 1:1250 (‘50-inch’) series, useful to engineering geologist, but not for normal fieldwork. These large scale maps show spot heights and bench marks, but no contours.
Maps are sold as paper copies but monochrome copies on transparent plastic can be supplied, printed on the reverse side to that geology can be plotted on the matt upper surface without damaging the topographic detail. All maps carry the National Grid. OS Maps can be bought from approved distributors throughout Britain but if in difficulty, or for special needs, contact: Ordnance Survey (Dept. LM), Romsey Road, Maybush, Southamton, SO9 4DH.
3.2.2 North America
The United States Geological Survey is responsible fro publishing most of the topographic maps of the USA. Maps are published of the US itself, Puerto rico, Guam, American Samoa and the Virgin Islands at 1:1,000,000, 1:250,000 and, in certain areas only, at 1:62,500 and 1:24,000. Special maps are also printed at other scales. A free descriptive booklet can be obtained from: National Cartographic Information Center, Geological Survey, Reston, Virginia 22092. Maps can be bought from the Branch of Distribution, Geological Survey, at either Arlington, Virginia 22202 or the Federal Center, Denver, Colorado 80225.
In Canada the situation is more complex because both the federal and provincial governments produce maps. Enquiries should be made to the Map Distribution Office, 615 Both Street, Ottawa 4. Maps likely to be used by field geologist are pulished at 1:250,000, 1:125,000 (in progress), 1:50,000 (in progress) and, in urban areas, 1:25,000.
Australia produces maps at 1:1,000,000 and 1:250,000, with incomplete coverage at 1:100,000 and 1:50,000. They are available from: Map Sales Section of the Department, Tasman House, P.O. Box 850, Canberrra City, ACT 2601; 460 Bourke Street, Melbourne, Victoria; and the Commonwealth Centre, Sidney, N.S.W, 2000. Maps and aerial photograph are also available from the Surveyor General, Department of Lands in each state or territorial capital, and also for Tasmania and Papua.
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