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Topographic Maps. Understanding Topographic Maps. Topographic maps are two-dimensional representations 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.
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Understanding Topographic Maps • Topographic maps are two-dimensional representations 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.
Understanding Topographic Maps • Topographic maps are tools used in geologic studies because they show the configuration of the earth’s 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.
Topographic Quadrangles • Quadrangles are sections of the Earth that are bounded by lines of • latitude at the top (north) and bottom (south) • Longitude on the right (east) and left (west)
Topographic Quadrangles • Longitude and latitude are measured in degrees, minutes and seconds. • 1 degree (o) = 60 minutes (‘) • 1 minute = 60 seconds (“)
Compass Bearing • A bearing is the direction from one point to another • If direction is expressed in degrees east or west of north, it is called a “quadrant bearing.” • If direction is expressed in degrees between 0 and 360, it is called “azimuth bearing.”
Quadrant Bearing N22oE What is the bearing from C to D?
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).
Contour Interval • The Contour Interval (CI) is the difference in elevation between two adjacent contour lines. • The CI can vary from map to map. Usually expressed in feet or meters. • Elevation is always referenced to Mean Sea Level (MSL). • MSL=0
Map Scale • several representations of scale exist • Verbal: “one inch equals one mile” • Ratio: 1:24,000 means that the portion of the earth represented has been reduced to 1/24000th its actual size. • Graphic
Change in elevation between 2 points Distance between 2 points Calculating Gradient (or Slope) Gradient is usually expressed as ft/mi. Gradient =
Topographic Profiles • topographic maps represent a view of the landscape as seen from above (called “map view”) • for producing a detailed study of a landform it is necessary to construct a topographic profile • a topographic profile is a cross-sectional view along a line drawn through a portion of a topographic map
Creating topographic profiles • Lay a strip of paper along a line across the area where the profile is to be constructed. • Mark on the paper the exact place where each contour, stream and hill top crosses the profile line. • Label each mark with the elevation of the contour it represents.
Creating topographic profiles • Prepare a vertical scale on profile paper by labeling the horizontal lines corresponding to the elevation of each index contour line. • Place the paper with the labeled contour lines at the bottom of the profile paper and project each contour to the horizontal line of the same elevation. • Connect the points.
Vertical Scale Horizontal Scale Vertical Exaggeration VE = Example: VE = 1:2000/1:4000= 2, which basically means... "the vertical relief of the terrain portrayed in this profile view is exaggerated two-fold relative to its actual profile in the real-world".
