# Maps as Models of the Earth Chapter 2 AC Earth Science 2009.

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Maps as Models of the Earth Chapter 2 AC Earth Science 2009

What Does Earth Really Look Like? A map is a representation of the features of a physical body such as Earth. The Greeks thought of Earth as a sphere almost 2,000 years before Columbus sailed in 1492. Around 240 BCE, Greek mathematician Eratosthenes calculated the circumference of the Earth. His calculation was wrong by only 6,250 km.

Finding Direction on Earth A reference point is a fixed place on the Earth’s surface from which direction and location can be described. The North and South Poles are used as reference points on the Earth. Cardinal Directions are the directions north, south, east, and west. Using cardinal directions is more precise than using directions such as “right” or “left.”

You Are Here! YOU ARE HERE!!!

Finding Direction… Using a Compass A compass is a tool that uses the natural magnetism of the Earth to show direction. A compass needle points to the magnetic north pole. Earth has two different sets of poles—the geographic poles and the magnetic poles.

Magnetic Declination Using Magnetic Declination Magnetic declination is measured in degrees east or west of true north. Magnetic declination has been determined for different points on the Earth’s surface, as shown below.

Latitude Latitude is the distance north or south of the equator. The equator is a circle halfway between the North and South Poles that divides the Earth into the Northern and Southern Hemispheres. Lines of latitude are parallel to the equator. Latitude is expressed in degrees.

Longitude Longitude is the distance east and west of the prime meridian. The prime meridian is the line that represents 0º longitude. It runs from the North Pole, through Greenwich, England, to the South Pole. Lines of longitude are not parallel. They touch at the poles and are farthest apart at the equator. Longitude is also expressed in degrees.

Models of Latitude and Longitude

How Do We Use It? Using Latitude and Longitude Lines of latitude and lines of longitude cross and form a grid system on globes and maps. This grid system can be used to find locations on the Earth’s surface.

A Flat Sphere? A map is a flat representation of the Earth’s curved surface. When you move information from a curved surface to a flat surface, you lose some accuracy. Changes called distortions happen in shapes and sizes of landmasses and oceans on map. Direction and distance can also be distorted.

Flat Sphere? Map Projections Mapmakers use map projections to move the image of Earth’s curved surface onto a flat surface. To understand how map projections are made, think a translucent globe that has a light inside. If you hold a piece of paper against the globe, shadows of marks on the globe appear on the paper. The way the paper is held against the globe determines the kind of map projection that is made.

Projection A cylindrical projection is a map projection that is made by moving the surface features of the globe onto a cylinder. The most common cylindrical projection is called a Mercator projection. A Mercator projection is accurate near the equator, but areas near the poles look wider and longer on the map than they look on the globe.

Projection… A conic projection is a map projection that is made by moving the surface features of the globe onto a cone. The cone touches the globe at each line of longitude but at only one line of latitude. There is no distortion along the line of latitude where the globe touches the cone. Areas near this line of latitude are distorted less than other areas are.

An azimuthal projection is a map projection that is made by moving the surface features of the globe onto a plane. The plane touches the globe at only one point. The point of contact is usually one of the poles. There is little distortion at the point of contact. However, distortion increases as you move away from the point of contact.

Equal-Area Projections A map projection that shows the area between latitude and longitude lines the same size as that area on a globe is called an equal-area projection. The shapes of the continents and oceans are distorted on equal-area projections. However, these projections are good for determining distance.

Examples…

Details Maps should have a title, a compass rose, a scale, a legend, and a date. Unfortunately, not all maps have all this information. The more of this information a map has, the more reliable the map is.

Modern Mapmaking Remote sensing is a way to collect information about something without physically being there. Remote Sensing and Satellites Remote sensors on satellites gather data about energy coming from Earth’s surface and send the data back to receiving stations on Earth.

Modern Mapmaking… Remote Sensing and Radar Radar is a tool that uses waves of energy to map Earth’s surface. The global positioning system (GPS) is a system of orbiting satellites that send radio signals to receivers on Earth. The receivers calculate latitude, longitude, and elevation. A geographic information systems (GIS) is a computerized system that allows a user to enter different types of information about an area.

Elements of Elevation A topographic map is a map that shows surface features, or topography, of the Earth. Topographic maps show natural and human-made features. Topographic maps also show elevation. Elevation is the height of an object above sea level. The elevation at sea level is 0.

Elements of Elevation Contour Lines are lines that connect points of equal elevation. Topographic maps use contour lines to show elevation. Contour Interval is the difference in elevation between one contour line and the next. Relief is the difference in elevation between the highest and lowest points of the area being mapped. Relief is used to determine the contour interval of a map.

Elements of Elevation… The spacing of contour lines indicate slope. Contour lines that are close together show a steep slope. Contour lines that are far apart show a gentle slope. An index contour is a darker, heavier line that is usually every fifth line and that is labeled by elevation.

Details… Topographic maps use symbols to represent parts of the Earth’s surface. Colors are also used to represent features. For example, cities and towns are pink, bodies of water are blue, and wooded areas are green.

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