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 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 fl at 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.

What is a landform?

There are many different landforms that can be identified. Using a map of the United States show the different land forms. The continental United States can be divided into three major parts, mountains in both west and east, with a plain in central U.S.

Maps with contours can help interpret these landforms. A mountain on a topographic map would have contours with high elevations. A steep mountain would have contours that are very close together.

You are on vacation and you want to take a long hike. The map you are using shows a direct route to where you want to go. As you walk, you find yourself talking to your friend and ?splash!? You are in a lake. The map you had did not show landforms, so you weren?t paying attention to where you were going. Understanding landforms can help you interpret maps. It is easy to walk up a gentle sloping mountain, but difficult to walk up a very steep canyon. A road can easily be built on flat land, but difficult to make a tunnel if you want to get through a mountain range.

What creates landforms?

Landforms are created by two different types of forces acting on the land: Those that affect the original surfaces and erosional elements. Volcanic and tectonic forces are the major contributors to the changing or "refacing" of original surfaces. The erosional elements (wind, water, ice, and heat) are responsible for dislodging, transporting, and depositing materials from the Earth. Most landforms are erosional.

The most notable landforms in the west are the Cascades, Sierra Nevada, Basin and Range, Colorado Plateau, and rocky Mountains. The central part includes the Great Plains and Central lowlands. The east has the Appalachian Plateau, the Piedmont and coastal plains.

As you take a hike you can notice different land features. But how did these landforms get that way? A landform is any feature of the Earth?s surface that is produced by nature. This includes plains, plateaus, mountain ranges, or valleys. Roads and streets produced by humans are not landforms.

The forces of nature that create landforms include water, ice, wind, volcanoes, and earthquakes. They are divided into landforms created by erosion and landforms created by tectonic activity.

Date: 2016-06-13; view: 314