Topographic maps TeacherWeb by benbenzhou


									Maps as Models of the Earth
Topographic Maps
• One of the most widely used maps is called a
  topographic map, which shows the surface
  features of Earth.

• topography the size and shape of
 the land surface features of a region

• elevation the height of an object above sea
Elevation on Topographic
• On topographic maps, elevation is shown by
  using contour lines.
• contour line a line that connects points of
  equal elevation on a map
• The difference in elevation between one
  contour line and the next is called the contour
  interval. The contour interval is selected
  based on the relief of the area being mapped.
Elevation on Topographic
• relief the difference between the
  highest and lowest elevations in a given
• Every fifth contour line is darker than
  the four lines one either side of it. This
  index contour makes reading elevation
Landforms on Topographic
• The spacing and direction of contour lines
  indicate the shapes of the landforms
  represented on a topographic map.
• Closely spaced contour lines indicate that the
  slope is steep.
• Widely spaced contour lines indicate that the
  land is relatively level.
Landforms on Topographic
Maps, continued
• A contour line that bends to form a V shape
  indicates a valley. The bend in the V points
  toward the higher end of the valley; this V
  points upstream, or in the direction from
  which the water flows, if there is a stream.
• Contour lines that form closed loops indicate
  a hilltop or a depression. Closed loops that
  have short straight lines perpendicular to the
  inside of the loop indicate a depression.
Topographic Maps,
The diagram shows how topographic maps
represent landforms.
Topographic Map Symbols
Topographic Map Symbols
• Symbols are used to show certain features on
  topographic maps.

• Symbol color indicates the type of feature.
  Constructed features, such as buildings, are
  shown in black. Highways are shown in red.
  Bodies of water are colored blue, and
  forested areas are colored green.
Index Contour, Contour
Interval, and Relief
Contour Lines
• Topographic maps use contour lines to
  indicate the shape and elevation of these
  landscape features because it is difficult, as
  we have already discovered, to show three-
  dimensional objects, like hills and valleys, on
  a two-dimensional surface, like a map.
• Contour lines are lines that connect
  the location of equal levels of
Contour Lines cont…
• If you are looking at a hill that is
  symmetrical, the contours will be almost
  round and become smaller and smaller
  towards the center of the hill as
  elevation increases
Contour Lines cont…
• If you are showing a hill with two peaks,
  your contour lines may look like this:
Contour Interval and Relief
• Contour Interval is the difference in
  elevation between one contour line and the
• Relief is the difference in elevation between
  the highest and lowest points of the area
  being mapped. Relief is used to determine
  the contour interval of a map.
Contour Intervals
• When terrain is flat, such as in prairie
  regions, contour intervals can have
  small values or increments, such as
  one or two meters so
  that even slight
  changes in the elevation of the
  landscape can be detected.
Contour Intervals and
• In mountainous or very hilly regions, such as
  the Rocky Mountains that border Alberta and
  British Columbia or the Laurentian Mountains
  in Quebec, contour intervals usually
  represent a greater vertical distance, such as
  fifty meters, so that the map isn't
  completely covered in contour
  interval lines.
              The Rocky Mountains
Contour Intervals
• Contour intervals that are closer together mean
  that there is a greater change in elevation over a
  shorter distance.

Mount Rainier located in Mount Rainier National
  Park, Washington, and its contour lines
Contour Lines

• Contour lines showing a steep and
  shallow gradient
• Another way of defining the change in elevation
  over a distance is to describe the slope.
• Topographic maps are useful tools in
  determining just how steep the land is, or how
  "fast" it rises or falls. Slope can be expressed in
  three ways: as a fraction, or ratio, referred to
  as a gradient; as a percentage, rise divided by
  the run multiplied by 100; and, as an angle
  expressed in degrees from the horizontal.
Spacing of Contour Lines
• The spacing of contour lines indicate
  slope. Contour lines that are close
  together show a steep slope. Contour
  lines that are far apart show a gentle
Index Counter
• An index contour is a darker, heavier
  line that is usually every fifth line and
  that is labeled by elevation.
Reading a Topographic Map

• Topographic maps use symbols to
  represent parts of the Earth’s surface.
  Colors are also used to represent
• Cities and towns are pink, bodies of
  water are blue, and wooded areas are
Golden Rules
• Contour lines never cross. All points
  along a contour line represent one
Golden Rules cont…
• The spacing of contour lines depends
  on slope characteristics. Contour lines
  that are close together show a steep
Golden Rules cont…
• Contour lines that cross a valley or
  stream are V shaped. The V points
  toward the area of highest elevation. If
  a stream or river flows through the
  valley, the V points upstream.
Golden Rules cont…
• The tops of hills, mountains, and
  depressions are shown by closed
  circles. Depressions are marked with
  short, straight lines inside the circle that
  point down slope to the depression.
Topographic Map
Breakdown of Areas of
   Breakdown of topographic
features including Contour Lines
Breakdown of features that are added from
aerial photographs and other sources, but
          are not field checked.

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