topographic maps

geologic maps

A geologic map shows the different rocks that are exposed at the surface of a region. Rock units are shown in a color identified in a key. On the geologic map of the Grand Canyon, for example, different rock types are shown in different colors. Some people call the Grand Canyon layer cake geology because most of the rock units are in layers. Rock units show up on both sides of a stream valley. A geologic map looks very complicated in a region where rock layers have been folded, like the patterns in marble cake. Faults are seen on this geologic map cutting across rock layers. When rock layers are tilted, you will see stripes of each layer on the map. There are symbols on a geologic map that tell you which direction the rock layers slant, and often there is a cut away diagram, called a cross section, that shows what the rock layers look like below the surface. A large-scale geologic map will just show geologic provinces. They do not show the detail of individual rock layers.

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bathymetric maps

Oceanographers use a type of topographic map that shows water depths (Figure 2.32). On this map, the contour lines represent depth below the surface. Therefore, high numbers are deeper depths and low numbers are shallow depths. These maps are made from depth soundings or sonar data. They help oceanographers understand the shape of bottoms of lakes, bays, and the ocean. This information also helps boaters navigate safely.

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interpreting contour maps

How does a topographic map tell you about the terrain? Lets consider the following principles: 1. The spacing of contour lines shows the slope of the land. Contour lines that are close together indicate a steep slope. This is because the elevation changes quickly in a small area. Contour lines that seem to touch indicate a very steep slope, like a cliff. When contour lines are spaced far apart the slope is gentle. So contour lines help us see the three-dimensional shape of the land. Look at the topographic map of Stowe, Vermont (Figure 2.28). There is a steep hill rising just to the right of the city of Stowe. You can tell this because the contour lines there are closely spaced. The contour lines also show that the hill has a sharp rise of about 200 feet. Then the slope becomes less steep toward the right. 2. Concentric circles indicate a hill. Figure 2.29 shows another side of the topographic map of Stowe, Vermont. When contour lines form closed loops, there is a hill. The smallest loops are the higher elevations on the hill. The larger loops encircling the smaller loops are downhill. If you look at the map, you can see Cady Hill in the lower left and another, smaller hill in the upper right. 3. Hatched concentric circles indicate a depression. The hatch marks are short, perpendicular lines inside the circle. The innermost hatched circle represents the deepest part of the depression. The outer hatched circles represent higher elevations (Figure 2.30). 4. V-shaped portions of contour lines indicate stream valleys. The V shape of the contour lines point uphill. There is a V shape because the stream channel passes through the point of the V. The open end of the V represents the downstream portion. A blue line indicates that there is water running through the valley. If there is not a blue line the V pattern indicates which way water flows. In Figure 2.31, you can see examples of V-shaped markings. Try to find the direction a stream flows. 5. Like other maps, topographic maps have a scale so that you can find the horizontal distance. You can use the horizontal scale to calculate the slope of the land (vertical height/horizontal distance). Common scales used in United States Geological Service (USGS) maps include the following: 1:24,000 scale - 1 inch = 2000 ft 1:100,000 scale - 1 inch = 1.6 miles 1:250,000 scale - 1 inch = 4 miles Including contour lines, contour intervals, circles, and V-shapes allows a topographic map to show three-dimensional information on a flat piece of paper. A topographic map gives us a good idea of the shape of the land.

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contour intervals

Since each contour line represents a specific elevation, two different contour are separated by the same difference in elevation (e.g. 20 ft or 100 ft.). This difference between contour lines is called the contour interval. You can calculate the contour interval by following these steps: a. Take the difference in elevation between 2 bold lines. b. Divide that difference by the number of contour lines between them. Imagine that the difference between two bold lines is 100 feet and there are five lines between them. What is the contour interval? If you answered 20 feet, then you are correct (100 ft/5 lines = 20 ft between lines). The legend on the map also gives the contour interval.

how do earth scientists use topographic maps

Earth scientists use topographic maps for many things: Describing and locating surface features, especially geologic features. Determining the slope of the Earths surface. Determining the direction of flow for surface water, groundwater, and mudslides. Hikers, campers, and even soldiers use topographic maps to locate their positions in the field. Civil engineers use topographic maps to determine where roads, tunnels, and bridges should go. Land use planners and architects use topographic maps when planning development projects, such as housing projects, shopping malls, and roads.

information from topographic maps

As we mentioned above, topographic maps show the shape of the land. You can determine a lot of information about the landscape using a topographic map. These maps are invaluable for Earth scientists.

what is a topographic map

Mapping is an important part of Earth Science. Topographic maps use a line, called a contour line, to show different elevations on a map. Contour lines show the location of hills, mountains and valleys. A regular road map shows where a road goes. But a road map doesnt show if the road goes over a mountain pass or through a valley. A topographic map shows you the features the road is going through or past. Lets look at topographic maps. Look at this view of the Swamp Canyon Trail in Bryce Canyon National Park, Utah (Figure 2.25). You can see the rugged canyon walls and valley below. The terrain has many steep cliffs with high and low points between the cliffs. Now look at the same section of the visitors map (Figure 2.26). You can see a green line that is the main road. The black dotted lines are trails. You see some markers for campsites, a picnic area, and a shuttle bus stop. The map does not show the height of the terrain. Where are the hills and valleys located? What is Natural Bridge? How high are the canyon walls? Which way do streams flow? A topographic map represents the elevations in an area (Figure 2.27). We mentioned topographic maps in the section on orienteering above.

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contour lines

Contour lines connect all the points on the map that have the same elevation. Lets take a closer look at this (Figure Each contour line represents a specific elevation. The contour line connects all the points that are at the same elevation. Every fifth contour line is made bold. The bold contour lines have numbers to show elevation. Contour lines run next to each other and NEVER cross one another. If the lines crossed it would mean that one place had two different elevations. This cannot happen.

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instructional diagrams

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questions

On a topographic map, only the contour lines that are numbered represent changes in elevation.

a. true

-->  b. false

A cross section

-->  a. can show the inside of something

b. is a type of topographic map

c. cannot used with bathymetric maps

d. uses concentric circles to show elevations

Two contour lines on a topographic may be parallel or they may intersect each other.

a. true

-->  b. false

Which is NOT true of a bathymetric map?

a. it is a type of topographic map

b. larger numbers show great depths

-->  c. negative numbers are used to show depths below sea level

d. it is often made using sonar

The contour interval of a topographic map represents the horizontal distance between contour lines.

a. true

-->  b. false

Contour lines that create a V shape indicate what?

-->  a. a stream channel

b. a hilltop

c. a valley

d. a cliff

Which of the following is a topographic map NOT able to do?

a. show the slope of an area

b. show the horizontal scale

-->  c. give details about the land use in an area

d. determine the direction of water flow

You can use a topographic map to determine the slope of the land.

-->  a. true

b. false

On a bathymetric map, contour lines represent the distance to the bottom of the water.

-->  a. true

b. false

If elevation between 2 bold lines is 1000 feet, and there are 5 lines in between the bold lines, what is the contour interval?

a. 5

-->  b. 200

c. 500

d. 2000

A topographic map can be used to determine the direction that rivers and streams flow.

-->  a. true

b. false

A topographic map of a mountain shows which side of the mountain is steepest.

-->  a. true

b. false

If contour lines are so close together that they almost touch, they represent a plain or plateau.

a. true

-->  b. false

Topographic maps are useful only to geologists and other Earth scientists.

a. true

-->  b. false

Geologic maps use different colors to represent different types of rocks.

-->  a. true

b. false

The difference between two contour lines is the contour interval.

-->  a. true

b. false

Contour lines help us to see the three-dimensional shape of the land.

-->  a. true

b. false

Concentric lines that are very far apart show a high, steep hill.

a. true

-->  b. false

The hatch marks on a topographic map are drawn on the side of the circle with the higher elevation.

a. true

-->  b. false

While topographic maps can show vertical distances, they cannot show horizontal distances.

a. true

-->  b. false

feature on a topographic map represented by concentric contour lines with hatch marks

a. contour interval

b. topographic map

c. contour line

-->  d. depression

e. river valley

f. bathymetric map

g. hill

map that shows water depths in a body of water

a. contour interval

b. topographic map

c. contour line

d. depression

e. river valley

-->  f. bathymetric map

g. hill

difference in elevation between adjacent contour lines on a topographic map

-->  a. contour interval

b. topographic map

c. contour line

d. depression

e. river valley

f. bathymetric map

g. hill

map that shows elevations of features on Earths surface

a. contour interval

-->  b. topographic map

c. contour line

d. depression

e. river valley

f. bathymetric map

g. hill

feature on a topographic map represented by concentric contour lines without hatch marks

a. contour interval

b. topographic map

c. contour line

d. depression

e. river valley

f. bathymetric map

-->  g. hill

line connecting points with the same elevation on a topographic map

a. contour interval

b. topographic map

-->  c. contour line

d. depression

e. river valley

f. bathymetric map

g. hill

feature on a topographic map represented by v-shaped contour lines

a. contour interval

b. topographic map

c. contour line

d. depression

-->  e. river valley

f. bathymetric map

g. hill

What is the contour interval on this metric topographic map?

a. 100 meters

b. 50 meters

-->  c. 20 meters

d. 10 meters

diagram questions

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