Transcript Maps As Models Of The Earth

Maps As Models Of The Earth
Mapping the Earth’s Surface
Globes
• The most accurate representation of the
entire surface of the Earth is a globe.
• A globe is a spherical, or round, model
of the Earth.
• It shows the shapes, sizes, and
locations of all the Earth’s land masses
and bodies of water.
What’s a Map?
• A map is a drawing of the Earth, or a
part of the Earth, on a flat surface.
• There are many ways to show the
Earth’s surface features on maps.
Some maps show only a small area of
the Earth.
• Others show the Earth’s entire surface.
• Maps are often grouped together in a
book called an atlas.
Types of Maps
• Maps show:
– locations and distances on the Earth’s
surface.
– different local features.
– soil types in an area.
– currents in the ocean.
Distortions
• Maps have one serious drawback.
Because they are flat, maps cannot
represent a round surface accurately.
• When you move information from a
curved surface to a flat surface, lose
some accuracy because changes occur
in the shapes and sizes of landmasses
and oceans. This is called distortion.
• Direction and distance can also be
distorted.
Map Projections
• Like a photograph of a person, a map is
only a projection, or a representation of
a three-dimensional object on a flat
surface.
• Mapmakers (cartographers) use map
projections to move the image of Earth’s
curved surface onto a flat surface.
Map Projections
• 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.
Another way to put it
• A map projection is a way to represent the
curved surface of the Earth on the flat surface
of a map.
• A good globe can provide the most accurate
representation of the Earth.
• A globe may not be practical for many of the
functions for which we require maps.
Map Projections
• Map projections allow us to represent
some or all of the Earth's surface, at a
wide variety of scales, on a flat, easily
transportable surface, such as a sheet
of paper.
• Map projections also apply to digital
map data, which can be presented on a
computer screen.
Classes of Map Projections and
Their Use
• There are several ways to classify the
wide variety of map projections. One of
the most common classifications is by
distortion characteristics:
– which properties of the Earth does the
projection maintain?
– Which does it distort?
Projection Characteristics
• An issue with all projections is that they
have to distort or change in some way
the representation of shape, area,
direction, or distance of land features in
one way or another in order to "flatten"
the globe to a piece of paper.
Projection Characteristics
• Some projections are good at keeping
the true shape of land features on a flat
map, but they make the representation
of distance on a map longer or shorter
than it is in real life, or the direction of
features is not correct, or maybe the
representation of the area of a country,
or ocean is not representative of the
actual area of that feature in real life.
How Do I Choose?
• As a map user, knowing all that you
now know about map projections,
how do you choose the right
projection?
• You must ask yourself questions
about what you are using the map
for.
• Are you calculating the distance from
your school to a school in a sister
city in Japan?
– You will probably choose an equidistant
map projection because it shows
distance correctly.
Area of Distortion
• Do you want to study how much land is used
for growing crops in India compared to
Australia?
– You will want to ensure that the area of these
countries is correctly represented and would be a
good choice.
Position
• Maybe you are just using a map to show where
your country is on a map. In this case, making
sure that the shape of the country is correct
and that it conforms to the shape represented
on a globe is important and would be best for
your purpose.
• It is important to remember that
whenever you choose to keep a true
representation of one characteristic,
either shape, areas, distance, or
direction, another characteristic is
changed or distorted.
• Only on a globe, which is spherical like
the Earth, can all these characteristics
be correctly represented.
Cylindrical Projections
• 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.
Cylindrical Projection
Conic Projections
• 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.
Conic Projection
Azimuthal Projections
• An azimuthal (also called planar) 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,
increases as you
from the point of contact.
distortion
move away
Azimuthal Projection
Equal-Area Projections
• 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.
Projections
• Maps and Globes: Maps and their uses
Information Shown on Maps
• 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.
Symbols
Symbols
• Symbols are commonly used on maps to
represent features such as cities, highways,
rivers, and other points of interest.
• Symbols may resemble the features that they
represent, or they may be more abstract.
• Symbols are commonly explained in a legend.
• legend a list of map symbols and their
meanings
Information on Maps
Map Scales
Map Scales
• scale the relationship between the distance shown on a
map and the actual distance
• Map scales are commonly expressed as graphic scales,
fractional scales, or verbal scales.
• A graphic scale is a printed line that has markings that
represent units of measure, such as meters or kilometers.
• A fractional scale is a ratio that indicates how distance on
Earth relates to distance on the map.
• A verbal scale expresses scale in sentence form.
Remote Sensing
• 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.
Remote Sensing and Radar
• 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.