DESCRIPTION OF THE TOPOGRAPHIC MAP OF THE UNITED STATES
The United States Geological Survey is making
a topographic map of the United States. This
work has been in progress since 1882, and more
than one-third of the area of the country, excluding
outlying possessions, has been mapped. The map-
ped areas are widely scattered, nearly every State being represented, as shown on the progress maps accompanying each annual report of the Director.
This great map is being published in atlas sheets of convenient size, which are bounded by parallels and meridians. The four-cornered division of land corresponding to an atlas sheet is called a quadrangle. The sheets are of approximately the same size: the paper dimensions are 20 by 16\frac{1}{4} inches; the map occupies about 17\frac{1}{4} inches of height and 11\frac{1}{2} to 16 inches of width, the latter varying with latitude. Three scales, however, are employed. The largest scale is 1:62500, or very nearly one mile to one inch; i. e., one linear mile on the ground is represented by one linear inch on the map. This scale is used for the thickly settled or industrially important parts of the country. For the greater part of the country an intermediate scale of 1:125000, or about two miles to one inch, is employed. A third and still smaller scale of 1:250000, or about four miles to one inch, has been used in the desert regions of the far West. A few special maps on larger scales are made of limited areas in mining districts. The sheets on the largest scale cover 15° of latitude by 15° of longitude; those on the intermediate scale, 30° of latitude by 30° of longitude; and those on the smallest scale, 1° of latitude by 1° of longitude.
The features shown on this map may, for convenience, be classed in three groups: (1) water, including seas, lakes, ponds, rivers and other streams, canals, swamps, etc.; (2) relief, including mountains, hills, valleys, cliffs, etc.; (3) culture, i. e., works of man, such as towns, cities, roads, railroads, boundaries, etc. The conventional signs used for these features are grouped below. Variations appear in some maps of earlier dates.
All water features are shown in blue, the smaller streams and canals in full blue lines, and the larger streams, lakes, and the sea by blue water-lining. Certain streams, however, which flow during only a part of the year, their beds being dry at other times, are shown, not by full lines, but by lines of dots and dashes. Ponds which are dry during a part of the year are shown by oblique parallel lines. Salt-water marshes are shown by horizontal ruling interspersed with tufts of blue, and fresh-water marshes and swamps by blue tufts with broken horizontal lines.
Relief is shown by contour lines in brown. Each contour passes through points which have the same altitude. One who follows a contour on the ground will go neither uphill nor downhill, but on a level. By the use of contours not only are the shapes of the plains, hills, and mountains shown, but also the elevations. The line of the seacoast itself is a contour line, the datum or zero of elevation being mean sea level. The contour line at, say, 20 feet above sea level is the line that would be the seacoast if the sea were to rise or the land to sink 20 feet. Such a line runs back into the valleys and forward around the points of hills and spurs. On a gentle coast this contour line is far from the present coast line, while on a steep slope it is near it. Thus a succession of these contour lines far apart on the map indicates a gentle slope; if close together, a steep slope; and if the contours run together in one line, as if each were vertically under the one above it, they indicate a cliff. In many parts of the country are depressions or hollows with no outlets. The contours of course surround these, just as they surround hills. Those small hollows known as sinks are usually indicated by hachures, or short dashes, on the inside of the curve. The contour interval, or the vertical distance in feet between one contour and the next, is stated at the bottom of each map. This interval varies according to the character of the area mapped; in a flat country it may be as small as 5 feet; in a mountainous region it may be 200 feet. Certain contours, usually every fifth one, are accompanied by figures stating elevation above sea level. The heights of many definite points, such as road corners, railroad crossings, railroad stations, summits, water surfaces, triangulation stations, and bench marks, are also given. The figures in each case are placed close to the point to which they apply, and express the elevation to the nearest foot only. The exact elevations of bench marks and their descriptions, as well as the descriptions and geodetic coordinates of triangulation stations, are published in the annual reports and bulletins of the Survey. The publications pertaining to specified localities may be had on application.
The works of man are shown in black, in which color all lettering also is printed. Boundaries, such as State, county, city, land-grant, reservation, etc., are shown by broken lines of different kinds and weights. Houses are shown by small black squares which in the densely built portions of cities and towns merge into blocks. Roads are shown by fine double lines (full for the better roads, dotted for the inferior ones), trails by single dotted lines, and railroads by full black lines with cross lines. Other cultural features are represented by conventions which are easily understood.
The sheets composing the topographic atlas are designated by the name of a principal town or of some prominent natural feature within the quadrangle and the names of adjoining published sheets are printed on the margins. They are sold at five cents each when fewer than 100 copies are purchased, but when ordered in lots of 100 or more copies, whether of the same or of different sheets, the price is three cents each.
The topographic map is the base on which the facts of geology and the mineral resources of a quadrangle are represented. The topographic and geologic maps of a quadrangle are finally bound together, accompanied by a description of the district, to form a folio of the Geologic Atlas of the United States. The folios are sold at twenty-five cents each, excepting that such as are unusually comprehensive are priced accordingly.
Applications for the separate topographic maps or for folios of the Geologic Atlas should be accompanied by cash—the exact amount—or by post-office money order, and should be addressed to—
THE DIRECTOR,
United States Geological Survey,
Washington, D. C.
February, 1911
CONVENTIONAL SIGNS
CULTURE (printed in black)
City or village
Roads and building
Metalliferous road (lines indicate on record maps only)
Private or secondary road
Trail or path
Railroads and stations
Electric railroad
Tunnel
Wharves
Breakwater and jetties
Bridges
Ferry
Ford
Dam
Canal lock
U. S. township and section lines and located corners
State line
County line
Coral township or district line
Non-evasion line
Land-grant line
City limits or borough line
Small park or cemetery line
Triangulation or primary traverse monument
U. S. mineral monument
Boundary monument
Bench mark (Temporary bench marks shown by brown crosses and black figures without lettering)
Cemeteries
Church, School
Coke ovens
Oil wells
Mine on quarry
Prospect
Shaft
Mine tunnel (showing direction of direction unknown)
Light-ship
Lighthouse or beacon
Life-saving station
RELIEF (printed in brown)
Figures (showing heights above mean sea level; when means not level datum, and horizontal lines, mentally determined, are omitted by the writer.)
Contours (showing height above mean sea level; also horizontal lines, mentally determined, are omitted by the writer.)
Depression contours
Levee
Wash
Cliffs
Mine dumps
Sand and sand dunes
STREAMS
Falls and rapids
Intermittent streams and ditches
Canals or ditches
Aqueducts or water-pipes
Aqueduct tunnel
Lakes or ponds
Unsurveyed streams and abandoned canals
Intermittent lakes
Glacier (Or shown by contours printed in blue.)
Spring
Salt marsh
Fresh marsh
Grassy pond
Tidal flat
WOODS (when shown, printed in green)