Maps as Models of the Earth TOPOGRAPHIC MAPS Topographic Maps • One of the most widely used maps is called a topographic map, which shows the surface features of Earth. • topography the size and shape of the land surface features of a region • elevation the height of an object above sea level Elevation on Topographic Maps • On topographic maps, elevation is shown by using contour lines. • contour line a line that connects points of equal elevation on a map • The difference in elevation between one contour line and the next is called the contour interval. The contour interval is selected based on the relief of the area being mapped. Elevation on Topographic Maps • relief the difference between the highest and lowest elevations in a given area • Every fifth contour line is darker than the four lines one either side of it. This index contour makes reading elevation easier. Landforms on Topographic Maps • The spacing and direction of contour lines indicate the shapes of the landforms represented on a topographic map. • Closely spaced contour lines indicate that the slope is steep. • Widely spaced contour lines indicate that the land is relatively level. Landforms on Topographic Maps, continued • A contour line that bends to form a V shape indicates a valley. The bend in the V points toward the higher end of the valley; this V points upstream, or in the direction from which the water flows, if there is a stream. • Contour lines that form closed loops indicate a hilltop or a depression. Closed loops that have short straight lines perpendicular to the inside of the loop indicate a depression. Topographic Maps, continued The diagram shows how topographic maps represent landforms. Topographic Map Symbols Topographic Map Symbols • Symbols are used to show certain features on topographic maps. • Symbol color indicates the type of feature. Constructed features, such as buildings, are shown in black. Highways are shown in red. Bodies of water are colored blue, and forested areas are colored green. Index Contour, Contour Interval, and Relief Contour Lines • Topographic maps use contour lines to indicate the shape and elevation of these landscape features because it is difficult, as we have already discovered, to show three- dimensional objects, like hills and valleys, on a two-dimensional surface, like a map. • Contour lines are lines that connect the location of equal levels of elevation. Contour Lines cont… • If you are looking at a hill that is symmetrical, the contours will be almost round and become smaller and smaller towards the center of the hill as elevation increases Contour Lines cont… • If you are showing a hill with two peaks, your contour lines may look like this: Contour Interval and Relief • Contour Interval is the difference in elevation between one contour line and the next. • Relief is the difference in elevation between the highest and lowest points of the area being mapped. Relief is used to determine the contour interval of a map. Contour Intervals • When terrain is flat, such as in prairie regions, contour intervals can have small values or increments, such as one or two meters so that even slight changes in the elevation of the landscape can be detected. Contour Intervals and Distance • In mountainous or very hilly regions, such as the Rocky Mountains that border Alberta and British Columbia or the Laurentian Mountains in Quebec, contour intervals usually represent a greater vertical distance, such as fifty meters, so that the map isn't completely covered in contour interval lines. The Rocky Mountains Contour Intervals • Contour intervals that are closer together mean that there is a greater change in elevation over a shorter distance. Mount Rainier located in Mount Rainier National Park, Washington, and its contour lines Contour Lines • Contour lines showing a steep and shallow gradient Slope • Another way of defining the change in elevation over a distance is to describe the slope. • Topographic maps are useful tools in determining just how steep the land is, or how "fast" it rises or falls. Slope can be expressed in three ways: as a fraction, or ratio, referred to as a gradient; as a percentage, rise divided by the run multiplied by 100; and, as an angle expressed in degrees from the horizontal. Spacing of Contour Lines • The spacing of contour lines indicate slope. Contour lines that are close together show a steep slope. Contour lines that are far apart show a gentle slope. Index Counter • An index contour is a darker, heavier line that is usually every fifth line and that is labeled by elevation. Reading a Topographic Map • Topographic maps use symbols to represent parts of the Earth’s surface. Colors are also used to represent features. • Cities and towns are pink, bodies of water are blue, and wooded areas are green Golden Rules • Contour lines never cross. All points along a contour line represent one elevation Golden Rules cont… • The spacing of contour lines depends on slope characteristics. Contour lines that are close together show a steep slope. Golden Rules cont… • Contour lines that cross a valley or stream are V shaped. The V points toward the area of highest elevation. If a stream or river flows through the valley, the V points upstream. Golden Rules cont… • The tops of hills, mountains, and depressions are shown by closed circles. Depressions are marked with short, straight lines inside the circle that point down slope to the depression. Topographic Map Breakdown of Areas of Woodland Breakdown of topographic features including Contour Lines Breakdown of features that are added from aerial photographs and other sources, but are not field checked.
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