NOTE.—The Geological Survey is making a topographic map of the United States-The sheets of which it is composed are projected without reference to political divisions, and are designated by some prominent town or natural feature found on them. 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 280, 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 about 17.5 inches in height by 11.5 to 16 inches in width, the latter varying with the latitude. A description of the topographic map is printed on the reverse of each sheet.
More than two-fifths of the area of the country, excluding outlying possessions, has been mapped, every State being represented. Massachusetts, Connecticut, Rhode Island, New Jersey, and the District of Columbia are completely mapped. Sheets of the regular size are sold by the Survey at 10c. each; but in lots of 50 or more copies, whether of the same sheet or of different sheets, the price is 6c. each. The discount is allowed on all orders the net cost of which amounts to $3.00 or more and applies on an order for either maps or folios alone or for maps and folios together, but does not apply to thefolios sold at 5c. each on account of damage by fire.