Maps as Models of Earth

WARMUP

Draw a map from your home to one of your favorite places. Clearly label all

landmarks and include information that might be useful to someone using the

map.

MAPS AS MODELS OF THE EARTH

Earth Science: Book G, Chapter 1

SECTION 1: YOU ARE HERE

By the end of this section, you should be able to:Explain how a magnetic compass can be used to find directions on Earth.

Explain the difference between true north and magnetic north.

Compare latitude and longitude.Explain how latitude and longitude are used to locate places on Earth.

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 EARTHA 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.”

FINDING DIRECTION ON EARTHA 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.

FINDING DIRECTION ON EARTHMagnetic 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.

FINDING LOCATIONS ON THE EARTH

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.

FINDING LOCATIONS ON THE EARTHLongitude 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.

FINDING LOCATIONS ON THE EARTHLines 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.

SECTION 1 REVIEW

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WARMUP

What is similar and what is different?

Write three possible uses for each map.

Write three improvements that could be made to each map.

SECTION 2: MAPPING THE EARTH’S SURFACE

By the end of this section, you should be able to:Explain why maps of the Earth show distortion.Describe four types of map projections. Identify five pieces of information that should be shown on a map.

Describe four methods modern mapmakers use to make accurate maps.

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.

A FLAT SPHERE?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 of 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.

A FLAT SPHERE?The way the paper is held against the globe determines the kind of map projection that is made.

PROJECTIONS OF THE EARTHA 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.

PROJECTIONS OF THE EARTHA 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.

PROJECTIONS OF THE EARTHA 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.

PROJECTIONS OF THE EARTHThere 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.

PROJECTIONS OF THE EARTHAn 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.

PROJECTIONS OF THE EARTHThe 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.

PROJECTIONS OF THE EARTHA 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.

PROJECTIONS OF THE EARTHThe shapes of the continents and oceans are distorted on equal-area projections. However, these projections are good for determining distance.

INFORMATION SHOWN ON MAPSMaps 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 MAPMAKINGRemote sensing is a way to collect information about something without physically being there.

Remote sensors on satellites gather data about energy coming from Earth’s surface and send the data back to receiving stations on Earth.

MODERN MAPMAKINGRadar is a tool that uses waves of energy to map Earth’s surface.

Radar Mapping Venus

MODERN MAPMAKINGThe 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.

MODERN MAPMAKINGA geographic information systems (GIS) is a computerized system that allows a user to enter different types of information about an area.

SECTION 2 REVIEW

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WARMUP

SECTION 3: TOPOGRAPHIC MAPS

By the end of this section, you should be able to:Explain how contour lines show elevation and landforms on a map.

Explain how the relief of an area determines the contour interval used on a map.

List the rules of contour lines.

ELEMENTS OF ELEVATIONA 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 ELEVATIONContour 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.

ELEMENTS OF ELEVATIONRelief 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 ELEVATIONThe 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.

ELEMENTS OF ELEVATIONAn index contour is a darker, heavier line that is usually every fifth line and that is labeled by elevation.

READING A TOPOGRAPHIC MAPTopographic 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

FOUR GOLDEN RULES OF CONTOUR LINESContour lines never cross.

The spacing of contour lines depends on slope characteristics.

Contour lines that cross a valley or stream are V-shaped.

Contour lines form closed circles around the tops of hills, mountains, and depressions.

SECTION 3 REVIEW

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