Models of the Earth Earth Science Chapter 3

Finding Locations of Earth Earth’s axis of rotation is used to establish reference points on Earth. Points at which Earth’s axis intersects on the surface are used as reference points (North & South Poles.) Halfway between the poles is a circle called the equator that divides the Earth into northern and southern hemispheres.

Latitude A set of circles drawn around the Earth is used to describe positions north and south of the equator. These circles are called latitude lines and they run parallel from east to west. The angular distance north or south of the equator is called latitude.

Degrees of Latitude Latitude is measured in degrees. Each 1° degree of latitude is equal to about 111 km. Each degree of latitude is divided into 60 minutes and is equal to about 1.85 km. Each minute is divided into 60 seconds A precise latitude would read 38°53’23”N. The equator is set at 0° latitude. The north and south poles are set at 90°.

Longitude East-west locations on the globe are established using meridians. A meridian is a semicircle that runs from pole to pole. The prime meridian runs through Greenwich, England and is 0° longitude. Longitude is the angular distance (degrees) east or west of the prime meridian.

Measuring with Longitude Meridian opposite of the prime meridian is set at 180° and is also called the international date line. All positions east of the prime meridian have longitudes between 0° and 180°E. All positions west of the prime meridian have longitudes between 0° and 180°W. The distance between degrees varies depending on the latitude because the lines get closer together as you move toward the poles.

Great Circles A great circle is any circle that divides the globe into halves or marks the circumference of the globe. Any circle formed by two meridians is a great circle. The route along a great circle is the shortest distance between two points on a sphere, therefore air and sea routes often follow great circles.

Finding Direction There are many tools for finding direction. Those tools include: Magnetic Compass: magnetic bar in compass indicates direction by interacting with Earth’s magnetic field GPS: global positioning satellites is a navigation system that uses 24 satellites that transmit radio signals to Earth’s surface

Reading a Map Maps are commonly drawn with north at the top and east on the right. Parallels should run from side to side and meridian should run from top to bottom. Many maps also include a compass rose which indicates the cardinal directions of north, south, east and west.

Map Symbols Maps often have symbols for cities, rivers, and roads. These symbols should be displayed in a legend. A legend is a list of the symbols and their explanations.

Map Scales A map must be drawn to scale to be accurate. The scale of a map indicates the relationship between distance shown on the map and actual distance. Scales are shown in three ways: Graphic scale Fractional scale: 1:25,000 Verbal scale: 1 cm equals 100 cm

Isograms A line on a map that represents a constant or equal value of a given quantity is called an isogram. Ex. Isotherms: connect locations of equal temperature Isobars: connect locations of equal atmospheric pressure Contour lines: locations of equal elevation

Topographic Maps A topographic map shows the surface features, or topography, of Earth. Topographic maps show both natural features and constructed features. A topographic map shows elevation, or height above sea level.

Advantages of Topographic Maps A topographic map provides more details about the surface of land that either a drawing or projection map. A topographic map shows: Size Shape Elevation

Elevation on a Topographic Map On topographic maps, contour lines are used to show locations of equal elevation. The shape of the contour lines reflect the shape of the land. The difference between elevation is called the contour interval and is set by the cartographer. Relief is the difference between the highest and lowest points of elevation. Every fifth contour line is made bold and is called a index contour.

Landforms on Topographic Maps The spacing and direction of contour lines indicates the shapes of landforms in a topographic map. Contour lines that are spaced far apart indicate land is relatively level. Contour lines close together indicate a steep slope. A v-shape indicates a valley. Closed loop contour lines indicate either hills or depressions.

Topographic Map Symbols Symbols such as color indicate different features. Some colors include: Brown: contour lines Black: major boundaries (county lines) Red : highways Blue: water Green: forested areas

Geologic Maps Geologic maps show the distribution of geologic features. Geologic features include: types of rock, locations of faults and folds and other structures. Geologic maps are usually shown on top of a base maps so that the geologic features are shown relative to roads.

Soil Maps Soil maps are used to classify and describe different types of soil. Soil maps are based on information gathered by soil surveys. A soil survey consists of three parts: text, maps, and tables. Soil maps are typically made by the NRCS and USDA and are very useful for agriculture and land management.

Soil Map of Earth