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Introduction to Earth and Maps

Verbal scale: One inch on the map represents 3,168,000 inches or __________ feet, or ____________ miles on

the ground.

13. Compare the fractional scale 1:10,000 to 1:3,168,000. Which would show MORE AREA?

14. Compare the fractional scale 1:10,000 to 1:3,168,000. Which would show MORE DETAIL?

Map Projections

Cartography, or mapmaking, is the study and practice of making representations of the Earth on a flat surface.

Cartographers design maps based on the properties they want to preserve and the information they want to portray.

A map projection is a systematic means to portray shape, area, distance, and direction of the Earth on a two-

dimensional surface. Map projections are created by projecting landmasses and the graticule onto a flat surface. All map

projections contain distortions since no one projection preserves all four properties simultaneously. A globe is the only

accurate representation of shape, area, distance, and direction of the Earth’s surface.

There are three main properties of projections. Equal area projections maintain equal area relationships; conformal

projections maintain angular relationships in order to preserve shape; and equidistant projections maintain distances

between points.

The class of a map projection can be conic, cylindrical, or planar. Conic-class maps result from wrapping a flat surface of

a cone around a reference globe and are often used to project the midlatitudes. Wrapping a cylindrical surface (a

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rectangle) around a globe creates a cylindrical-class map. Cylindrical-class maps are usually centered on the equator. A

planar-class map results from placing a flat surface next to the surface of a globe, so that the two only touch at a single

point, and is most often used to project the poles.

In order to reduce some of the distortion created by projecting a map, cartographers center their maps on a standard

line or point. The points where the developable surface (flat piece of paper with no tears) touches the globe creates the

standard line or point where distortion is minimal. Distortion increases as you move away from the standard line or

point. Generally, cylindrical projections employ the equator as the standard line and thus are greatly distorted in the

higher latitudes. Conical projections typically have a standard line somewhere in the midlatitudes, so this type of

projection is often used for the United States. Planar projections typically have a single standard point because the

developable surface of the plane contacts the globe in only one place.

15. List two advantages that a globe has compared to a map.

16. List two advantages that a map has compared to a globe.

Figure 6 Mercator, Peters, and Goode’s projections

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17. The Mercator projection (conformal cylindrical equatorial) maintains the correct shape of landmasses, but not

their sizes. As a result, Greenland (0.8 million square miles) appears larger than the entire continent of Africa

(11.6 million square miles). The Peters projection (equal area cylindrical equatorial) maintains the correct size of

countries, but not their shapes. Goode’s projection maintains the size and shape of landmasses, but interrupts

the oceans. Are you more accustomed to viewing one of these in particular? How do these maps influence your

perception of the world?

18. Take a look through pages 12-13 in Goode’s World Atlas (if you have the 23rd edition, pages xvi and xvii). These

pages describe and show examples of the main map projections used in the atlas. List one benefit and one

drawback specific to Goode’s Interrupted Homolosine Equal Area Projection (also shown above in Figure 6).

19. What is a map projection?

Types of Maps

Look over the thematic map types on pages 14-15 (or xviii-xix in newer edition) and types of map projections on pages

12-13 (xvi and xvii) in Goode’s World Atlas to answer the following:

20. What type of thematic map are the temperature maps on pages 32-33 (or in 23rd edition, pages 22-23)? Select

one of the following:

a. Choropleth map

b. Isoline map

c. Area class map

21. On page 39 (or page 30 in 23rd edition), examine the map of carbon dioxide emissions.

a. What type of thematic map is this?

b. What does the size of the circle represent?

c. What does the color of the circle represent?

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22. On the Rock Type map pp. 96-97 (or in 23rd edition, the Geology map on pages 42-43), would the Colorado

Plateau appear larger or smaller at a scale of 1:1,000,000?

23. Looking at the Rock Type of the US map on pages 96-97 (42-43 in newer edition), can you discern which rock

type is more common at the surface (igneous, metamorphic, or sedimentary)?

Isoline and Topographic Maps

A topographic map displays the relative positions and elevations of physical features on the Earth’s surface. The

United States Geological Survey (USGS) publishes topographic maps for the United States in a variety of sizes

and scales (ranging from 1:24,000 to 1:1,000,000). The most commonly used scale of a topographic map is

1:24,000, which covers an area measuring 7.5 minutes latitude by 7.5 minutes longitude and is referred to as a

7.5-minute quadrangle.

An isoline is a line that connects points of equal value, and contour lines are a specific type of isoline that

connect points of equal elevation. Contours are usually printed in brown on topographic maps, and index

contours are heavier brown lines usually marked with the elevation. The contour interval is the change in

elevation between contours, and varies from map to map.

Figure 5 Contour lines and a corresponding landscape.

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Contour Line Characteristics:

• A contour line represents only one elevation.

• Contour lines do not divide or split.

• Contour lines do not end. They may run off maps that represent only a small portion of the landscape.

• Contours are closer together on steep slopes and farther apart on gentler slopes. On vertical slopes,

contour lines will overlap, but they never cross each other.

• Contour lines bend upstream into an inverted “V” when crossing streams, and bend downslope when

crossing ridges.

• Hatchured contours indicate a depression. The hatchured lines have small tick marks on the downhill

side.

Examine the map of Lake Contouria with elevational points. The 170 foot contour has already been drawn. Draw the

remaining contour lines at intervals of 10 feet. Be sure that all points with a lower elevation than the contour line you

are drawing are on the downhill side of the line. Use a pencil and draw lightly until you are sure the contour positions

are correct, then darken the lines. The inverted “V”s should coincide with the stream channels.