HOG HUNTING STRATEGIES
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    Topographic
    Map
    Symbols
    U.S. Dept. of  the Interior
    U.S. Geological Survey

    What is a Topographic Map?
         A map is a representation of the Earth, or part of it. The
    distinctive characteristic of a topographic map is that the
    shape of the Earth’s surface is shown by contour lines.
    Contours are imaginary lines that join points of equal
    elevation on the surface of the land above or below a
    reference surface, such as mean sea level. Contours
    make it possible to measure the height of mountains,
    depths of the ocean bottom, and steepness of slopes.  

         A topographic map shows more than contours. The map
    includes symbols that represent such features as streets,
    buildings, streams, and vegetation.  These symbols are
    constantly refined to better relate to the features they
    represent, improve the appearance or readability of the map,
    or reduce production cost.

         Consequently, within the same series, maps may have
    slightly different symbols for the same feature.  Examples of
    symbols that have changed include built-up areas, roads,
    intermittent drainage, and some lettering styles. On one type
    of large-scale topographic map, called provisional, some
    symbols and lettering are hand drawn.

    Reading Topographic Maps
        Interpreting the colored lines, areas, and other symbols is
    the first step in using topographic maps. Features are
    shown as points, lines, or areas, depending on their size
    and extent. For example, individual houses may be shown
    as small black squares. For larger buildings, the actual
    shapes are mapped. In densely built-up areas, most
    individual buildings are omitted and an area tint is shown.
    On some maps, post offices, churches, city halls, and other
    landmark buildings are shown within the tinted area.

         The first features usually noticed on a topographic map
    are the area features, such as vegetation (green), water
    (blue), and densely built-up areas (gray or red).

        Many features are shown by lines that may be straight,
    curved, solid, dashed, dotted, or in any combination. The
    colors of the lines usually indicate similar classes of
    information: topographic contours (brown); lakes, streams,
    irrigation ditches, and other hydrographic features (blue);
    land grids and important roads (red); and other roads and
    trails, railroads, boundaries, and other cultural features
    (black). At one time, purple was used as a revision color to
    show all feature changes. Currently, purple is not used in our
    revision program, but purple features are still present on
    many existing maps.

        Various point symbols are used to depict features such as
    buildings, campgrounds, springs, water tanks, mines,
    survey control points, and wells.

         Names of places and features are shown in a color
    corresponding to the type of feature. Many features are
    identified by labels, such as “Substation” or “Golf Course.”

         Topographic contours are shown in brown by lines of
    different widths. Each contour is a line of equal elevation;
    therefore, contours never cross. They show the general
    shape of the terrain. To help the user determine elevations,
    index contours are wider. Elevation values are printed in
    several places along these lines. The narrower
    intermediate and supplementary contours found between
    the index contours help to show more details of the land
    surface shape. Contours that are very close together
    represent steep slopes. Widely spaced contours or an
    absence of contours means that the ground
    slope is relatively level. The elevation difference between
    adjacent contour lines, called the contour interval, is selected
    to best show the general shape of the terrain. A map of a
    relatively flat area may have a contour interval of 10 feet or
    less. Maps in mountainous areas may have contour intervals
    of 100 feet or more. The contour interval is printed in the
    margin of each U.S. Geological Survey (USGS) map.

         Bathymetric contours are shown in blue or black,
    depending on their location. They show the shape and slope
    of the ocean bottom surface. The bathymetric contour interval
    may vary on each map and is explained in the map margin.
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