A ratio compares two numbers by division. For example, the scale of a map given as a ratio is 1:250,000. At this scale, the distance between two points on the map measures23.5 cm. How would you find the actual distance? 1. Write the scale as a fraction. 2. Write a proportion. Let d represent the distance between the two points. 3. Write the cross products. 1 Xd = 250,000 X 23.5 cm d = 5,875,000 cm - Models of Earth Scales and Ratios

Practice Problem A map’s scale is 1:25,000. If two points are 4.7 cm apart on the map, how far apart are they on the ground? 117,500 cm or 1.175 km; (1 X d = 25,000 X 4.7 cm) or (25,000 X 4.7 cm) - Models of Earth Scales and Ratios

- Models of Earth An Earth Reference System • Distances around circles are measured in degrees.

- Models of Earth An Earth Reference System • The equator and prime meridian divide Earth’s surface into hemispheres.

- Models of Earth Locating Points on Earth’s Surface • The lines of latitude and longitude form a grid that can be used to find locations anywhere on Earth.

- Models of Earth Locating Points on Earth’s Surface • Every point on Earth’s surface has a particular latitude and longitude.

- Models of Earth Map Projections • A Mercator projection is based on a cylinder with grid lines that has been flattened. On a Mercator projection, lines of longitude are parallel, so shapes near the poles are distorted.

- Models of Earth Map Projections • An equal-area projection shows areas correctly, but distorts some shapes around its edges.

- Models of Earth Map Projections • A conic projection is based on a cone that covers part of Earth and is then rolled out flat. A conic projection’s grid is formed from straight lines of longitude and curved lines of latitude.

- Models of Earth Asking Questions • Before you read, preview the red headings. In a graphic organizer like the one below, ask a question for each heading. As you read, write answers to your questions. Question Answer What is meant by an Earth reference system? Just like a checkerboard, a grid system is needed to locate points on Earth. How do you locate points on Earth’s surface? Lines of latitude and longitude can be used to locate any place. Why are there different types of map projections? Different types are useful for different purposes.

- Models of Earth Latitude and Longitude • Click the Video button to watch a movie aboutlatitude and longitude.

- Models of Earth Links on Latitude and Longitude • Click the SciLinks button for links on latitude and longitude.

End of Section:Models of Earth

- Maps and Computers Identifying Main Ideas • As you read the section “Maps and Computers,” write the main idea in a graphic organizer like the one below. Then write three supporting details that further explain the main idea. Main Idea Computers use digitized data to make maps. Detail Detail Detail Digitizing is converting the location of map points to numbers. Much of the data is gathered by satellites. The Global Positioning System (GPS) is used to find latitude, longitude, and elevation.

- Maps and Computers More on Satellite Mapping • Click the PHSchool.com button for an activityabout satellite mapping.

End of Section:Maps and Computers

- Topographic Maps Mapping Earth’s Topography • Mapmakers use contour lines to represent elevation, relief, and slope on topographic maps.

- Topographic Maps Topographic Map Activity • Click the Active Art button to open a browser window and access Active Art about topographic maps.

- Topographic Maps Reading a Topographic Map • To read a topographic map, you must familiarize yourself with the map’s scale and symbols and interpret the map’s contour lines.

- Topographic Maps Mapping Elevation Data • The map shows the elevation data points on which the contour lines are based. Study the map and the map key, then answer the questions.

100 feet Reading Maps: What is the contour interval on this map? - Topographic Maps Mapping Elevation Data

Yellow; points below 1,200 feet. Reading Maps: What color are the lowest points on the map? What range of elevations do these points represent? - Topographic Maps Mapping Elevation Data

Red; 1,500 feet or above. Reading Maps: What color are the highest points on the map? What range of elevations do these points represent? - Topographic Maps Mapping Elevation Data

1,300 feet Applying Concepts: What is the elevation of the contour line labeled A? - Topographic Maps Mapping Elevation Data

Valley; contour lines curve uphill. Inferring: Is the area between B and C a ridge or a valley? How can you tell? - Topographic Maps Mapping Elevation Data

At point D, elevation is above 1,500 feet. It then decreases to about midway along the trail where elevation is less than 1,400 feet. Elevation then increases again to point C, which is above 1,500 feet. Interpreting Data: Describe how elevation changes along the trail from point D to point C. - Topographic Maps Mapping Elevation Data

- Topographic Maps Using Prior Knowledge • Before you read, write what you know about topographic maps in a graphic organizer like the one below. As you read, write what you learn. What You Know Some maps show where mountains and plains are. Many people use maps to plan a trip or hike in unfamiliar areas. What You Learned Mapmakers use contour lines to represent elevation, relief, and slope on topographic maps A map’s scale and symbols can help you to interpret the map’s contour lines. Topographic maps have many uses in science and engineering, business, government, and everyday life.

End of Section:Topographic Maps

include with which may be with with with Graphic Organizer Landforms Mountains Plains Plateaus High elevation, low relief High elevation, high relief Coastal Interior Low to high elevation, low relief Low elevation, low relief

End of Section:Graphic Organizer

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