NOTE.—The Geological Survey is making a topographic map of the United States. The individual maps of which it is composed are projected without reference to political divisions, and each map is designated by the name of some prominent town or natural feature in the area mapped. Three scales are ordinarily used, 1: 62,500, 1: 125,000, and 1: 250,000. These correspond approximately, to 1 mile, 2 miles, and 4 miles to 1 linear inch, covering, respectively, average areas of 230, 920, and 3,700 square miles. For some areas of particular importance, special large-scale maps are published. The usual size, exclusive of the margin, is 17.5 inches in height by 11.5 to 16 inches in width, the width varying with the latitude. The sheets measure 20 by 16½ inches. A general description of the topographic maps is printed on the reverse of each sheet.
More than two-fifths of the area of the country, excluding Alaska, has been mapped, every State being represented. Connecticut, Delaware, the District of Columbia, Maryland, Massachusetts, New Jersey, Ohio, Rhode Island, and West Virginia are completely mapped. Maps of the regular size are sold by the Survey at 10c. each, but a discount of 40 per cent is allowed on any order which amounts to $5.00 or more at the retail price. The discount is allowed on an order for either maps or folios alone or for maps and folios together, but does not apply to a few folios that are sold at 5c. each on account of damage by fire.