Transcript Slide 1

Topographic Maps
September, 2011
MAP
• A model of Earth’s surface.
• Best model is a globe (no distortion).
• Flat maps are made but they usually contain
some distortion (like flattening an orange
peel).
• The smaller the area drawn (or of curvature)
the less the distortion.
FIELDS
• Any region of space that has some measurable
value of a specific quantity at a specific
location.
• Temperature, pressure, wind speed, humidity,
elevation, etc.
• Most change with time (dynamic).
Representation of Fields
ISOLINE – a line that connects equal values
in a field.
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Types include . . .
Isotherms – connect equal temperatures.
Isobars – connect equal pressures.
Contour Lines – connect equal elevations.
GRADIENT
• The rate at which a field changes from one
place to another (over a distance).
GRADIENT
10 miles
Gradient = 10°F/10 miles = 1°F/mile
2 miles
Gradient = 10°F/2 miles = 5°F/mile
• The closer the isolines, the steeper or greater the
gradient.
• The further apart the isolines, the gentler or lesser
the gradient.
TOPOGRAPHIC MAPS
• A two-dimensional model of Earth’s surface
that shows elevation at various locations.
• Also called Contour Maps.
Rules For Reading Topographic Maps
1. Topographic maps have lines on the surface connecting
points of equal elevation (contour lines).
Rules For Reading Topographic Maps
2. The difference in elevation between any two adjacent
contour lines in the contour interval.
CONTOUR
INTERVAL:
10,600
100 meters
Rules For Reading Topographic Maps
3. Hill tops are indicated by closed loops.
What is the highest contour line? _________________
10,700
What is the highest elevation of the hill?
____________________________________________
Must be above 10,700 but below 10,800
Rules For Reading Topographic Maps
4. A bench mark is a location whose exact elevation is
known and is noted on a brass aluminum plate.
Rules For Reading Topographic Maps
5. Topographic maps
are usually oriented
so that North is at
the top.
6. Many maps have
map scales at the
bottom to show
linear distance.
Rules For Reading Topographic Maps
7. Depressions are
usually indicated by
closed loops with
hachured lines
inside.
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The first line of a
depression contour
has the same value
as the contour line
just crossed before
the depression was
come upon.
Rules For Reading Topographic Maps
8. Contour lines
bend to form a
“V” in a valley
with the point of
the “V” pointing
uphill. A stream
always flows
out of the “V” if
it crosses a
contour line.
Rules For Reading Topographic Maps
9. The spacing of contour lines can show gradient. The
closer the contour lines, the steeper the gradient. The
further apart the contour lines, the gentler the
gradient.
B to C = Steep Gradient
A to B = Lesser Gradient
C to D = Least Gradient
GRADIENT =
22°F
28°F – 22°F
3 meters
28°F
= 2°F/meter
40
PROFILES
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A side view of a section of a contour map showing
the slopes in the region.
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