Objectives: -Explain how topographic maps use contour lines to show elevation
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Transcript of Objectives: -Explain how topographic maps use contour lines to show elevation
Chapter 3 Section 3Topographic Maps (note to teacher: have topographic map ready
and don’t close it until lecture is over)
Objectives:-Explain how topographic maps use contour lines to show elevation-Describe topographic map symbols-Demonstrate how to use topographic maps to determine the shape of the land, the flow of rivers, and distance
Topography -
• The natural and human-made surface features of an area.
Topographic Maps
• Common type is the 7.5 minute map commonly called a quadrangle, that spans 7.5 minutes of latitude and 7.5 minutes of longitude
• Topographic Map of Sedona
7.5 Minute Map
• Has a scale of 1:24,000– (one inch represents 2,000 ft.)
Topographic Maps Con’t
• Contour lines – narrow brown lines that indicate elevation
• Topo
• Contour Interval – The difference in elevation between consecutive contour lines.
• contour interval 40
Calculating Contour Interval
• Subtract 2 adjacent bold contour lines and divide by the number of lines
• 200-100=100• 5 contour lines
• 100/5=20• C.I. = 20 ft
Slope
• The distance between one contour line and the next indicates steepness.
• Contour lines that are close together = steep• Contour lines with space between them =
gradual • Rise/Run = average slope
Green represents vegetation Blue represents water
Bench Marks
• The exact location where elevation is known and noted on a brass or aluminum plate which is permanently set into the ground
• On a map it is noted with “BM” next to a X with the elevation given.
• benchmark
Army Corps of Engineers Bench Marks
USGS Bench Mark
Geodetic Bench Mark
Spot Elevations
• Elevations of road forks, hilltops, lake surfaces, and other points of interest.
• Marked with small crosses “+”• spot elevations
Understanding Symbols
• Contour lines that form circles indicate hills or mountains
• Depression contours indicate a depression in the landscape
Other features
• Contour lines that cross a river from an arrow which points toward the source
• Human made features are depicted in black• Thickly settled regions are pink
Magnetic Declination
• The angle by which a compass needle will vary from true north