Topographic Maps Topographic Maps

September, 2011September, 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

• Types include . . .

• Isotherms – connect equal temperatures.

• Isobars – connect equal pressures.

• Contour Lines – connect equal elevations.

ISOLINE – a line that connects equal values in a field.

GRADIENT• The rate at which a field changes from one

place to another (over a distance).

GRADIENT

• The closer the isolines, the steeper or greater the gradient.

• The further apart the isolines, the gentler or lesser the gradient.

10 miles 2 miles

Gradient = 10°F/10 miles = Gradient = 10°F/2 miles =1°F/mile 5°F/mile

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.

CONTOURINTERVAL:

10,10010,400

10,300

10,200

10,60010,700 100 meters

22°C24°C

26°C

28°C

18°C

32°C

Rules For Reading Topographic Maps

3. Hill tops are indicated by closed loops.

What is the highest contour line? _________________What is the highest elevation of the hill? ____________________________________________

10,700

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.

• 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.

Cold Creek

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 =

28°F – 22°F3 meters

= 2°F/meter

22°F

28°F

120

140

16018

0

80 60 40

20

0

220240260

280

280

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360380

180200220 120

10080

PROFILES• A side view of a section of a contour map showing

the slopes in the region.

3900

980

960

1000980

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10401020

980

1060

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1080

11001100

1120

11201140

0

130

530

510

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510

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480470

510

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XX

X

X

X X

X

X

X

530

510

520

510

520530

540

560

490

480470

510

500

X

X

X X

XX

X

X

X

X

650640

630

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610600

590

620

630