## Older Precambrian

pcgril Zoroaster Granite Pcgnt Trinity Gneiss pcvs Vishnu Schist

 Table 2.1 Interactive Table To explore Types of Maps and Projections more about maps and Projections, visit qlencoe.com. Map or Projection Common Uses Distortions Mercator projection navigation of planes and ships The land near the poles is distorted. Conic projection road and weather maps The areas at the top and bottom of the map are distorted. Gnomonic projection great circle routes The direction and distance between landmasses is distorted. Topographic map to show elevation changes on a flat projection It depends on the type of projections used. Geologic map to show the types of rocks below the surface present in a given area It depends on the type of projection used.

Three-dimensional maps Topographic and geologic maps are two-dimensional models of Earth's surface. Sometimes, scientists need to visualize Earth three-dimensionally. To do this, scientists often rely on computers to digitize features such as rivers, mountains, valleys, and hills.

### Map Legends

Most maps include both human-made and natural features located on Earth's surface. These features are represented by symbols, such as black dotted lines for trails, solid red lines for highways, and small black squares and rectangles for buildings. A map legend, such as the one shown in Figure 2.11, explains what the symbols represent. For more information about the symbols in map legends, see the Reference Handbook.

^P Reading Check Apply If you made a legend for a map of your neighborhood, what symbols would you include?

### Map Scales

When using a map, you need to know how to measure distances. This is accomplished by using a map scale. A map scale is the ratio between distances on a map and actual distances on the surface of Earth. Normally, map scales are measured in SI, but as you will see on the map in the GeoLab, sometimes they are in measured in different units such as miles and inches. There are three types of map scales: verbal scales, graphic scales, and fractional scales.

 Interstate U.S. highway State highway — Scenic byway ---- Unpaved road Railroad lllllllll River - Tunnel ) ( Lake/reservoir o Airport National Park, monument, or historic site f Marina 4» Hiking Lrail iiiiiiiiiiiiiii School, church Depression contour lines CsP Academic vocabulary Ratio the relationship in quantity, amount, or size between two or more things The ratio of girls to boys in the class was one to one Verbal scales To express distance as a statement, such as "one centimeter is equal to one kilometer," cartographers and Earth scientists use verbal scales. The verbal scale, in this example, means that one centimeter on the map represents one kilometer on Earth's surface. Graphic scales Instead of writing the map scale out in words, graphic scales consist of a line that represents a certain distance, such as 5 km or 5 miles. The line is labeled, and then broken down into sections with hash marks, and each section represents a distance on Earth's surface. For instance, a graphic scale of 5 km might be broken down into five sections, with each section representing 1 km. Graphic scales are the most common type of map scale. ^p Reading Check Infer why an Earth scientist might use different types of scales on different types of maps. Fractional scales Fractional scales express distance as a ratio, such as 1:63,500. This means that one unit on the map represents 63,500 units on Earth's surface. One centimeter on a map, for instance, would be equivalent to 63,500 cm on Earth's surface. Any unit of distance can be used, but the units on each side of the ratio must always be the same. A large ratio indicates that the map represents a large area, while a small ratio indicates that the map represents a small area. A map with a large fractional scale such as 1:100,000 km would therefore show less detail than a map with a small fractional scale such as 1:1000 km.