Maps as Models of Earth

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.

Earth Science: Book G, Chapter 1

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.

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.

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.”

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 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 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 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.

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.

What is similar and what is different?
Write three possible uses for each map.
Write three improvements that could be made to each
map.

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 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.

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.

The way the paper is held against the globe determines the
kind of map projection that is made.

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.

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.

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.

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.

Remote 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.

Radar is a tool that uses waves of energy to map Earth’s
surface.
Radar Mapping Venus

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.

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.

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.

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.

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.

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

Contour 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.

Maps as Models of Earth

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