California Water Resources Using a
Web-Based Geographic Information System
September 19, 2009
INTRODUCTION TO TOPOGRAPHIC MAPS
(Source: Richard Sedlock, SJSU BAESI/Geology)
A topographic map displays the relief of a landscape.
Relief is the range in elevation within an area of Earth’s surface.
Elevation is the vertical variation from a datum, or fixed “starting point” (usually, sea level).
What part of the world does the map show?
Title
Location (inset)
Adjacent quadrangles (either in box or along map edges)
Who made this map, anyway?
Date of original map and photorevisions, if any
Mapping agency
Grid systems
Latitude and longitude
Universal Transverse Mercator (UTM)
What are these curved lines?
They are contour lines that connect points of equal elevation.
index (every 5th line is heavier)
The map also shows “spot elevations” on peaks, at benchmarks, and at some other locations.
What else does this map show?
Scales: verbal, graphical, bar [map scale = map distance/Earth distance]
Vegetation type
Cultural information
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Rules for Understanding Topographic Maps
Contour lines connect points of equal elevation.
The horizontal spacing of the contour lines indicates the steepness of the Earth’s surface: steeper
slopes have more closely spaced contour lines.
The vertical spacing of contour lines is constant on a given map. The elevation two adjacent contour
lines is the contour interval (labeled at bottom center of map).
A given contour line generally is roughly parallel to adjacent contour lines.
Contour lines can never cross.
Hills or ridges are shown by “concentric” closed loops.
Depressions/craters are shown by closed loops with hachures pointing inward.
Where contour lines cross rivers, form a V that points upstream.
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The USGS supplies topographic maps, a guide to symbols, a tutorial, and lesson ideas:
http://education.usgs.gov/common/lessons/teaching_with_topographic_maps.html
Notes:
1. Ordering instructions for maps and guide to symbols are about one full screen down
2. 7.5’ USGS topographic maps now cost $8/map; educator discounts have been discontinued.
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Topographic Maps: General Questions (can be asked for any quadrangle)
1. What is the contour interval of the map? ___________
2. What latitude line marks the northern boundary of the map? ________________
3. What latitude line marks the southern boundary of the map? ________________
4. What longitude line marks the eastern boundary of the map? ________________
5. What longitude line marks the western boundary of the map? ________________
6. Express the distance from the northern to the southern boundary in miles ____________
in degrees, minutes, seconds _____________
7. Express the distance from the eastern to the western boundary in miles ____________
in degrees, minutes, seconds _____________
8. What is the magnetic declination of this map? _______________
9. In what year was the magnetic declination determined? ________________
10. In what year was the map published? ______________
11. What is the fractional scale of this map? __________________
12. One inch on the map equals ___________________________________on the ground.
13. What is the full name of this quadrangle? ____________________________________
14. What is the name of the quadrangle to the east of this quad? __________________________
15. What is the name of the quadrangle to the southwest of it? __________________________
16. What is the elevation of the highest point on this map? ________________
17. What is the elevation of the lowest point on this map? ________________
18. What is the total relief on this map? _______________
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Questions Specific to the Montara Mountain Quadrangle
1. What is the contour interval of the map? _________________
2. What is the longitude of the eastern edge of the map? ___________________
3. What is the latitude of the southern edge of the map? ____________________
4. What is the highest point on this map? ________________________
What is its elevation, in feet? _____________
5. What quadrangle lies directly south of this map?
________________________
Northeast of this map? _________________________
6. What is the elevation of the highest point on Cahill Ridge? _________________
7. What is the elevation of San Francisco International Airport? _______________
8. What is the biggest elevation drop, in feet, over a horizontal distance of 1000'?________
What is the average surface slope, or gradient, over this distance? ________________
9. What is the elevation of Montara Knob? _____________
10. Which is steeper, the north slope or south slope of Montara Knob? ______________
How do you know?
11. The San Andreas fault zone (misleadingly labeled as a “rift zone” on this map) coincides
with a pronounced northwest-trending valley. Faults commonly have such topographic
expression.
In which direction does surface water flow in the San Andreas fault zone on this map? [Hint:
note elevations of San Andreas Lake and Crystal Springs Reservoir] _____________
12. How far from the San Andreas fault zone is the nearest major engineered freeway? ________
13. In what direction does Vicente Creek (lower left of map) flow?_________________
How do you know?
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