1. Topographic Maps
September, 2011

2. 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.

4. 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).

5. Representation of Fields
ISOLINE – a line that connects equal values in a field.
Types include . . .
Isotherms – connect equal temperatures.
Isobars – connect equal pressures.
Contour Lines – connect equal elevations.

9. GRADIENT
The rate at which a field changes from one place to another (over a distance).

10. GRADIENT The closer the isolines, the steeper or greater the gradient.
10 miles
2 miles
Gradient = 10°F/10 miles =
1°F/mile
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.

11. TOPOGRAPHIC MAPS
A two-dimensional model of Earth’s surface that shows elevation at various locations.
Also called Contour Maps.

12. Rules For Reading Topographic Maps
Topographic maps have lines on the surface connecting points of equal elevation (contour lines).

13. Rules For Reading Topographic Maps
The difference in elevation between any two adjacent contour lines in the contour interval.
10,200
10,100
10,300
CONTOUR
INTERVAL:
10,400
10,600
100 meters
10,700

14. 18°C
22°C
24°C
26°C
28°C
32°C

15. Rules For Reading Topographic Maps
Hill tops are indicated by closed loops.

16. 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

17. Rules For Reading Topographic Maps
A bench mark is a location whose exact elevation is known and is noted on a brass aluminum plate.

18. Rules For Reading Topographic Maps
Topographic maps are usually oriented so that North is at the top.
Many maps have map scales at the bottom to show linear distance.

19. Rules For Reading Topographic Maps
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.

20. Rules For Reading Topographic Maps
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

21. Rules For Reading Topographic Maps
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

22. GRADIENT =
22°F
28°F – 22°F
3 meters
= 2°F/meter
28°F

23. 360
380
320
340
280
320
300
260
280
240
220 20
180
160
140
120 80 60 40
220
120
200
100
180 80

24. PROFILES
A side view of a section of a contour map showing the slopes in the region.
3900

27. 980
1020
1040
1100
1120
1100
1080
1140
1120
1060
1040
1020
980
960
1080
1060
980
1000

30. 130

32. 530
520
530
540
510
560
520
500
510
490
510
480
470

33. X X X X X X X X X

34. 530
520
530
540
510
560
520
500
510
490
510
480
470

36. 650
640 X X
630 X X
620 X X
610 X X
600 X X
590

37. 620
630