THE TOPOGRAPHIC MAPS OF THE UNITED STATES The United States Geological Survey is making a topographic atlas of the United States. This work has been in progress since 1882, and more than 38 per cent of the area of the country, excluding outlying possessions, has now been mapped. The areas mapped are widely distributed, every State being represented, as shown on the progress maps accompanying each annual report of the Director. This atlas is being published in sheets of convenient size, about 161 by 20 inches. The four-sided area of land represented on an atlas sheet is bounded by parallels and meridians and is called a quadrangle. The quadrangles mapped cover 1° of latitude by 1° of longitude, 30° of latitude by 30° of longitude, or smaller areas, the size of the area mapped depending on the scale used. Several scales are employed. The smallest scale, that used for quadrangles covering 1°, is 1:250,000, or very nearly 4 miles to an inch—that is, 4 linear miles on the ground is represented by 1 linear inch on the map. This scale is used for maps of the desert regions and some other parts of the far West. For the greater part of the country, which is mapped by quadrangles covering 30°, a larger scale, 1:125,000, or about 2 miles to an inch, is employed. A still larger scale, 1:62,500, or about a mile to an inch, is used for quadrangles covering 15°, the unit selected for mapping thickly settled or industrially important areas. A fourth scale, 1:31,680, or one- half mile to an inch, is employed for maps that are to be used in connection with irrigation or drainage, and a few maps of mining districts are published on still larger scales. A topographic survey of Alaska has been in progress since 1898 and nearly 30 per cent of its entire area has now been mapped. One-third of the area mapped, or 10 per cent of the Territory, has been covered only by reconnaissance work, the results of which have been mapped on a scale of about 10 miles to an inch. The maps of nearly all the remaining two-thirds of the surveyed area have been published on a scale of 1:250,000, or about 4 miles to an inch. These maps are large, each representing 22° of latitude by 4° of longitude. A few All water features are printed in blue, the smaller streams and canals in full blue lines and the larger streams, lakes, and the sea in blue water-lining. Intermittent streams—those whose beds are dry at least three months in the year—are shown by lines of dots and dashes. Relief is shown by contour lines in brown. A contour on the ground passes through points that have the same altitude. One who follows a contour will go neither uphill nor downhill but on a level. The contour lines on the map show not only the shapes of the hills, mountains, and valleys but also their elevations. The line of the sea coast itself is a contour line, the datum or zero of elevation being mean sea level. The contour at, say, 20 feet above sea level would be the shore line if the sea were to rise or the land to sink 20 feet. On a gentle slope this contour is far from the present coast; on a steep slope it is near the coast. Where successive contour lines are far apart on the map they indicate a gentle slope; where they are close together they indicate a steep slope; and where they run together in one line they indicate a cliff. The manner in which contour lines express altitude, form, and grade is shown in the figure below. [illegible] The United States Geological Survey is making a topographic atlas of the United States. This work has been in progress since 1882, and its results consist of published more than 42 per cent of the country, exclusive of possessions. This topographic atlas is published in the form of sheets measuring about 161 by 20 inches. Under the plan adopted the country is divided into quadrangles, the quadrangles are mapped on different scales, the scale for each map being that which is best adapted to the development of the country, and consequently, standard maps are of nearly uniform size, they repeat of different sizes. On the lower margin of each map a graphic scales showing distances in feet, meters, and in addition, the scale of the map is shown by a fraction of a fixed ratio between linear measurements on the map responding distances on the ground. For example, 1:250,000 means that 1 unit on the map (such as 1 inch, 10 meter) represents 62,500 similar units on the earth’s level. The heights of many points, such as road cor- marks, surfaces of lakes, and bench marks, are also given in figures, which express the elevations to the foot only. More exact elevations of bench marks, geodetic coordinates of triangulation stations, are pub- bulletins issued by the Geological Survey. A bul- taining to any State may be had on application. The works of man are shown in black, in which those county, city, land grant, township, or reservation, by by continuous or broken lines of different kinds and Public and through roads are shown by fine dou- private and poor roads by dashed double lines; trails single lines. Each quadrangle mapped for the topographic atlas ated by the name of a principal town or some natural feature within the quadrangle, and on the map the maps are printed the names of adjoining quad- which atlas sheets have been published or are in The sheets are sold at 10 cents each in lots of less copies or at 6 cents each in lots of 50 or more copies of the same or different sheets. The topographic map is the base on which the ge- the mineral resources of a quadrangle, and a few A topographic survey of Alaska has been in prog- 1898, and nearly 43 per cent of its area has now been 1. Surveys of areas in which there are problems of public importance—relating, for example, to mineral development, irrigation, or reclamation of swamp areas—are sufficient accuracy to be used in the publication of maps of a scale of 1:250,000 (1 inch = one-half mile), with a contour interval of 1, 5, or 10 feet. 2. Surveys of areas in which there are problems of public importance, such as most of the basin of the Mississippi and its tributaries, are made with sufficient accuracy to in the publication of maps on a scale of 1:63,360 (1 inch = 1 mile), with a contour interval of 10 to 25 feet. 3. Surveys of areas in which the problems are of public importance, such as much of the mountain region of Arizona or New Mexico, are made with accuracy to be used in the publication of maps on a scale of 1:250,000 (1 inch = nearly 2 miles), with a contour interval of 100 feet.