Hill on a topographic map
A topographic map, simply put, is a two-dimensional representation of a portion of the three-dimensional surface of the earth. Topography is the shape of the land surface, and topographic maps exist to represent the land surface. Topographic maps are tools used in geologic studies because they show the configuration of the earths surface. Cartographers solve the problem of representing the three-dimensional land surface on a flat piece of paper by using contour lines, thus horizontal distances and vertical elevations can both be measured from a topographic map. General Information Map Scale: Maps come in a variety of scales, covering areas ranging from the entire earth to a city block (or less). Vertical Scale (contour interval): All maps have a horizontal scale. Topographic maps also have a vertical scale to allow the determination of a point in three dimensional space. Contour Lines: Contour lines are used to determine elevations and are lines on a map that are produced from connecting points of equal elevation (elevation refers to height in feet, or meters, above sea level). The following are general characteristics of contour lines:
On most topographic maps, index contour lines are generally darker and are marked with their elevations. Lighter contour lines do not have elevations, but can be determined by counting up or down from the nearest index contour line and multiplying by the contour interval. The contour interval is stated on every topographic map and is usually located below the scale. Creating topographic profiles: Remember that topographic maps represent a view of the landscape as seen from above. For producing a detailed study of a landform it is necessary to construct a topographic profile or cross-section through a particular interval. A topographic profile is a cross-sectional view along a line drawn through a portion of a topographic map. A profile may be constructed quickly and accurately across any straight line on a map by following this procedure:
Stream Gradient: Stream gradient can also be determined from a topographic map. The gradient of a steam or river is determined by measuring a section of a stream or river and dividing the distance (in miles) into the vertical difference (in feet) between the two points. The result is expressed in feet per mile (ft./mi.). The equation used is:
Tips for Interpreting Topographic Maps Determining hillslope: Among other things, a topographic map can be used to measure the average slope of a hill (or hills).
Topographic Map Example |