Transcript Chapter 3 Section 3 Topographic Maps

Chapter 3 Section 3
Topographic 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