Transcript Map Projection Notes

Map Types & Projections: Notes
• Why do we use maps?
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Many can be stored at once
Easier (than a globe) to carry
Can have special purposes
Scales allow different levels of detail
What do
you think?
• What are the limitations of maps?
– Globe is 3D, maps are 2D.
– 2D will lead to distortion for shapes, distances, sizes, and
directions
VS.
Different Types of Maps
• Different types of maps try to protect from
different distortions
• Conformal
The shapes of places are accurate.
• Distance
Measured distances are accurate.
• Area/Equivalence
The areas represented on the map are proportional to their
area on the earth.
• Direction
Angles of direction are portrayed accurately.
Maps from Different Shapes
• Planar
– Good: polar maps, minimal distortion at the center,
show directions & distance well
– Bad: edges have distorted area, shape; only shows
half of the world at once
• Cylindrical
– Good: navigation, show direction and distance well,
showing the whole world
– Bad: distort shape & area near the poles (check out
Greenland & Antarctica)
• Conic (a compromise)
– Good: mid-latitude maps like the US and Europe,
showing a smaller area
– Bad: adds distortion of all aspects, but attempts to
keep each at a minimum
Planar Map
Cylindrical Map
USA: Cylindrical Map
Conic Map
USA: Conic Map
USA: Conic & Cylindrical
Draw the Map Types
• On your note-sheets, draw the map types to
the best of your ability.
Describe if the
following are Planar,
Cylindrical, or Conic
Interrupted Projection
These types of maps try to depict the continents as
accurately as possible by leaving blank space in the less
important areas of the map.
Common Map Projections
Even the same types of maps can become
different projections (or representations)
Azimuthal Equal-Area
Mercator
Azimuthal Equidistant
Robinson
Robinson Projections
How do these map projections differ?
Azimuthal
Equal-Area
Changes a sphere to a
disk
- Shows the size of
areas correctly
- Does not represent
angles correctly
Mercator
Standard map for
nautical purposes b/c
easy to plot a course
across an ocean.
- Shows shape of
areas correctly
- Accurate near the
equator but
becomes distorted
along the poles
(distorts these
areas)
Azimuthal
Equidistant
Map for showing
airline distances
- Attempts to show
distances, &
direction
accurately
- Useful for polar
projections but
distorts area &
shapes the fuller
you get from the
center point.
Robinson
Projection used to
show the whole world
at once (the
compromise map)
- Tries to reduce all
types of distortion
in size, shape,
direction, &
distance.
- Distortion at the
poles
Projections: Discussion Questions
• So, what map projections should we use
most often?
• How do map projections affect our
perception of the world?
Mercator Projection
(Google maps uses this)
Peters Map Projection
The Controversy Over Projection Types
What’s an accurate map?
Mercator
• Cons:
– Centers the world on Europe
– Inflates the northern areas at
the expense of the equatorial
regions
• Pros:
– Easy to travel across an
ocean: represents lines of
constant course
Peters
• Cons:
– Created for political purposes,
not cartography (lacks data)
– Distorts the shape of
continents
• Pros:
– Peters: "the Mercator
projection overvalues the
white man and distorts the
picture of the world to the
advantage of the colonial
masters of the time“
What can you conclude from this comparison?
Summarize each projection in your own words.
• How big is Greenland?
• On this Mercator projection Greenland and
South America appear similar in size.
• The inset map shows that South America is
actually about 15 times larger than
Greenland.
How big is Africa?
Greenland appears to be
the same size as Africa, yet
the land mass of Africa is
actually 14 times larger:
How big is Europe?
And compare Europe vs.
South America (3.8
million square miles vs.
6.9 million square miles):
The Mercator map distorts the relative size of the north and the
south. The south is actually more than twice as large (38.6 million
square miles to 18.9 million square miles)
Why were cartographic decisions made this way?
Where are the majority of third world nations located?
Why does the ‘Northern’ hemisphere HAVE to be at the top
of the map?
Could we change the world by changing our map?
Special Purpose Maps
• Also called thematic maps – they cover one
theme in a region
– Train lines, postal codes, population density,
precipitation, elevation, etc.
Special Purpose Maps: Types
• Choropleth: different colors are used to show
different values
• Isarithmic/contour: have lines that connect
regions with similar values & themes
• Dot: each dot represents a certain number of
some occurrence or feature
• Proportional symbol: varying sizes of a symbol
represent the real difference in some occurrence
or feature
Dot
Isarithmic/contour
Proportional Symbol
Choropleth
A Special Purpose Example: Topography
• A map with lines and symbols representing
the natural and man-made features of a part
of the earth’s surface. They show the location
and shapes of mountains, valleys, plains, etc.
Why would this be a useful map for hikers, or engineers?
Maps: Reflection
• Describe two (2) ways that a special purpose
map could be used to represent something
from the state of Connecticut.