Name ______________________
Date ___________________________
Earth Science
Topographic Maps Lab
INTRODUCTION: A map is a graphic representation of a surface drawn to scale. Maps can show the stars in the
heavens, the depth of water in a lake, the surface features on Mars, atmospheric pressure across a region, the geology of
an area, as well as numerous other applications. In general all maps represent 1) geographic location, 2) direction, and
3) dimension (horizontal and/or vertical distance). In this lab you will be working with topographic maps.
Topography means “the shape of the land”. Topographic maps are two-dimensional graphical representations of the
three-dimensional shape of the Earth’s surface, drawn to scale. Each topographic map shows the width, length and
variable height of the land above a datum or reference plane. The most commonly used datum is average sea level
(Tarbuck, Lutgens, and Pinzke, 2000). Earth scientists routinely use topographic maps for determining locations,
identifying landform types, elevations and other physical data.
GEOGRAPHIC LOCATION: “An international system for locating features on the surface of the Earth is a grid of
east-west lines of latitude and north-south lines of longitude (Figure 1). The system uses the geographic north and
south poles and the equator as location references. Distances are measured in fractions of a circle (in degrees).
Remember that all circles can be divided into 360. A degree of latitude or longitude can be divided into 60 minutes
(60’) and each minute can be divided into 60 seconds (60”).
The reference location for latitude is the equator, a circle defined by points halfway between the geographic north and
south poles, dividing the Earth into the Northern Hemisphere and the Southern Hemisphere (Figure 1). Latitude
indicates distances north and south of the equator. The measurement units are degrees, with the equator at 0 and the
poles at 90. The east-west lines of latitude are termed parallels because they are parallel to one another.
At the international Meridian Conference of 1884, the meridian passing through the Royal Astronomical Observatory
in Greenwich, England (near London) was chosen as the prime meridian. All longitudinal positions are measured from
this reference. Longitude increases both east and west from 0 at the prime meridian to 180 at the International Date
Line on the opposite side of the Earth. Unlike lines of latitude, the meridians of longitude are neither parallel nor
equally spaced except along a line of latitude. Because the meridians converge at the poles, the ground distance
represented by a degree or minute of longitudinal varies.” (Judson, Bonini, Rhodes, and Rossbacher, 2000).
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Name ______________________
Date ___________________________
Figure 1
QUESTION 1: Based on the above reading, fill in the blanks.
a) Lines of _______________________ run in an east-west direction and measure distances _________________
and ________________ of the equator.
b)
Lines of _______________________, known as meridians, converge at the poles.
c)
0 latitude is located at the ___________________.
d)
0 longitude is located at the ____________________.
e)
Lines of ____________________ are parallel to one another.
f) A degree of latitude or longitude can be divided into __________ minutes and each minute into ___________
seconds.
g)
Are all ground distances represented by a degree or minute the same (yes or no)? ________________________
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Name ______________________
Date ___________________________
QUESTION 2: Fill in the latitude and longitude of the following features on the Manlius, NY Quadrangle. Make sure
you indicate the direction of your coordinates.
Feature
FM High School
Latitude
Longitude
Round Lake
Bolivar Road School
DIRECTION: “Because most topographic maps cover pieces of latitude and longitude, the edges of the maps are true
north-south and east-west lines. The direction from one point to another can be determined with a protractor.
However, this is not necessarily the compass direction between the points. The magnetic North Pole, toward which
compass needles point, is not the same place as the geographic North Pole (the rotational axis of the Earth). The
angular difference between true geographic north and magnetic north is the magnetic declination. Because declination
varies from place to place and over time, a symbol and explanation is printed in the lower margin of most topographic
maps. The symbol shows the magnetic declination at the center of the map at a particular time.
Within the conterminous United States, magnetic declinations vary from about 22 West in Maine to 24 East in
Washington State (Figure 2). The magnetic declination must be considered if exact directions are needed when
navigating toward distant destinations. Sailors, geologists, and backcountry hikers all need to know the exact magnetic
declination to use their compass properly.
On magnetic declination diagrams from U.S. Geological Survey topographic maps, the star representative of the North
Star, shows the direction of geographic north centered on the north rotational pole of the Earth. MN means magnetic
north. The angle between the two lines is the magnetic declination. Because magnetic declination varies with time, the
date at which the declination was measured is provided. GN is grid north.” (Judson, Bonini, Rhodes, and Rossbacher,
2000)
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Name ______________________
Date ___________________________
Figure 2
QUESTION 3: What is magnetic declination?
QUESTION 4: When would you need to adjust for magnetic declination?
QUESTION 5: What is the magnetic declination provided on the Manlius, NY Quadrangle?
Magnitude ___________________
Direction ____________________
DIMENSION: The scale of a map is the relationship between a distance on a map and an actual distance on the
Earth’s surface. Map scales are commonly expressed in three ways:
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Name ______________________
Date ___________________________
1) Graphical Scales or Bar Scales: These graphically show the scale of the map by graduated lines. They are typically
provided to show distances in miles, feet, and kilometers. If a map is enlarged or reduced, this type of scale
remains valid.
2) Fractional Scales: This type of scale is often expressed as a representative fraction or R.F. For example:
R.F. = 1:48,000 = 1/48,000
This scale means that one unit of distance on the map, regardless of what unit is used (inches, centimeters, feet),
represents a distance equal to 48,000 of the same units on the ground. If a map is reduced or enlarged, the
fractional scale of the original map will not apply to the reduction or enlargement.
3) Verbal Scales: This type of scale provides another explanation of the relationship between distance on a map and
the ground distance. For example:
A map scale of 1:48,000 could verbally be described as having a scale of “1 inch equals 48,000 feet.”
Use the Manlius, NY Quadrangle to answer QUESTIONS 6-8.
QUESTION 6: What is the fractional scale of the map?
QUESTION 7: Express the map scale as a verbal scale in miles.
QUESTION 8: How long is Duguid Road in miles?
Contour Lines: “Topographic maps depict the shape of the land’s surface by using contour lines. A contour line
connects points that are at the same height above sea level. When you walk along a contour line, the shoreline of a lake
for example, you stay at the same elevation, going neither uphill nor down. Contours are drawn at specified elevations.
The vertical distance between contour lines is the contour interval. The difference in elevations between the highest
and lowest points in an area, the total relief, and the scale of the map determine what contour interval is used.
The spacing between the contours on a map shows the slope of the land. The closer together the contours are the
steeper the slope, and the farther apart they are, the gentler the slope. We generally assume that the ground surface
slopes uniformly between contours.
The contour interval of topographic map will be printed somewhere on it, commonly below the graphical bar scales.
Index contours have their elevation printed at various places along them and are shown as thicker lines than the other
contours. Intermediate contour lines are shown between the index contours. They, like index contours, represent
elevations that are multiples of the contour interval, but their elevations are not printed on the map.
In addition to contours, topographic maps also supply some other elevation data. Spot elevations are printed at various
places on most maps, and carefully surveyed positions, known as benchmarks, are also shown.” (Judson, Bonini,
Rhodes, and Rossbacher, 2000)
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Name ______________________
Date ___________________________
Use the Manlius, NY Quadrangle to answer QUESTIONS 9-13.
QUESTION 9: What is the contour interval used on this map?
QUESTION 10: Locate the highest and lowest elevations on the map. Note the elevations and briefly describe their
locations below (a verbal description is fine, you do not need to find latitude and longitude).
a) Highest elevation ___________________
Location:
b) Lowest elevation ___________________
Location:
QUESTION 11: Find FM High School.
a) In what direction is it located in relation to Fayetteville?
b) Based on the map how can you tell that FM High School is near the top of a hill?
QUESTION 12: Which is higher in elevation, the FM High School or the radio tower just over the Madison County
border in the southeast corner of the map?
QUESTION 13: Which side of Green Lake has a steeper slope?
Slope and Gradients: Slope is defined as the change in vertical distance divided by the horizontal distance. For
example:
vertical distance =
Slope = horizontal distance
80 ft
500 ft
= 0.16 or 16%
Notice that the units of measurement (ft/ft) cancel each other out, so that slope has no dimensions.
The slope of a river, the stream gradient, is commonly given in units of feet per mile (ft/mi.). Gradients are calculated
using the following formula:
Gradient =
Difference in elevation (ft) =
length of stream segment (mi)
40 ft = 7.3 ft/mi
5.5 mi
Relief: Relief refers to the difference in elevation between any two points. Maximum relief designates the difference
in elevation between the highest and lowest points in a given area.
Use the Manlius, NY Quadrangle to answer Questions 14-16.
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Name ______________________
Date ___________________________
QUESTION 14: Find the gradient from the top of the hill marked A to the stream in the valley between hill A and B.
QUESTION 15: Find the gradient from the top of the hill marked B to the stream in the valley between hill A and B.
QUESTION 16: Using your answer to QUESTION 10, calculate the maximum relief of the map. Show your
calculations.
Constructing a Contour Map: The next question asks you to construct your own contour map with a given set of data
points. Before your start carefully read the following rules and instructions. Remember that contour lines show the
elevation of points and connect all the points that have the same elevation.
Rules for Using Contour Lines
1. Contours of different elevations cannot cross each other. (Because all points on a single contour
have the same elevation, contours crossing demand two different elevations at the same point.)
2. Contours do not split or join.
3. Contours do not end except at the edges of a map or by closing on themselves.
4. A series of closed concentric contours indicate a hill or mountain.
5. Concentric hachured contours depict a closed depression.
6. Contours form V’s where they cross rivers. The point of the V is directed upstream (uphill).
QUESTION 17: Using the attached map, complete the contouring using a 20-foot contour interval.
Please Note:
1. A point will lie on a contour line ONLY is it is a multiple of 20, thus a data point of 40 will lie on
the 40 contour line, a data point of 42 will not.
2. Even the most practiced contourer doe a lot of erasing, USE A PENCIL!!!
References:
Judson, Sheldon; Bonini, William; Rhodes, Dallas; and Rossbacher, Linda. 2000. The Lab Book: Problem Solving in
Geology, second edition. Prentice Hall, N.J.
Tarbick, Edward; Lutgens, Frederick; and Pinzke, Kenneth. 2000. Applications & Investigations in Earth Science, third
edition. Prentice Hall, N.J.
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Name ______________________
Date ___________________________
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