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