distortion of maps
TRANSCRIPT
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Distortion of Maps
APHG
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What is a map?
• A map is a generalization or
representation of the real world
-Geoid: actual shape of the Earth which is
round and oblate (slightly squashed)
- Maps contain distortions: cannot represent
the three-dimensional Earth on a flat
surface without reconfiguration from
correct shape/reality
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Maps continue…
1) Map scale – most maps are smaller than
the reality they represent & map scale
tells us how much smaller; tells
relationship between distance on map
and distance on Earth’s surface
2) Map type – you can display the same
information on different types of maps
ex. thematic, dot, cartogram, etc.
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What is ratio scale?
• Ratio scale: ratio of map distance to Earth
distance
– 1:10,000 means that one inch on the map equals
10,000 inches on Earth’s surface, one centimeter
represents 10,000 centimeters, one foot equals
10,000 feet.
– Recall a small fractions has a large denominator so
that 1:100,000 is smaller scale than 1:25,000.
– A large-scale map depicts a small area with great
detail. A small-scale map depicts a larger area with
little detail.
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RATIO SCALE
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Which is the large-scale map?
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What is verbal scale?
• Verbal scale – translates the
representative fraction into words
– One inch represents one mile conveys more
meaning than 1:63,360
– Used little in places where people use metric
system
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What is graphic scale?
• Graphic scale – is a simple bar scale that
portrays distance on the map
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What is a map projection?
• Map projection: the way we fit Earth’s three-dimensional surface onto a flat surface; distortion in either area, direction, distance or shape
• Equal-area projections: portrays areas on the Earth’s surface in their true proportions but can distort shape
• Conformal projections: retains correct shape of small areas; latitude/longitude cross at right angles and scale is the same in all directions at any point on the map
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Mercator Projection
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Mercator Projection…
• Developed in 1569 by Gerardus Mercator as a navigation tool; ex. of conformal projection
• The meridians are equally spaced, parallel vertical lines, and the latitude lines are parallel, horizontal straight lines, spaced farther and farther apart as their distance from the Equator increases
• Shapes are correct for all areas, and map has correct directional relationships
• Advantage: Direction and shape are accurate Disadvantage: Size is distorted increasingly to the north or south of Equator.
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Mollweide Projection
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Mollweide Projection
• Create in 1800s by Karl B. Mollweide and
is an example of an equal-area projection
• Advantage: Accurate depiction of area
• Disadvantage :distorts shapes
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Robinson Projection
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Robinson Projection
• Frequently used
• Distorts both size and shape, but not too
much
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What are some different types of
maps?
• A thematic map depicts a single feature, for ex.:
climate, population, landform, land use, etc.
• Types of thematic maps:
– Isoline (Isopleth) – connects points of equal value
– Choropleth – puts features into classes and then
maps classes for each region
– Proportional symbol (Graduated circle) – size of the
symbol corresponds to the magnitude of the mapped
feature
– Dot – each dot represents some frequency
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MAP TYPES Isoline (isopleth) choropleth
Dot distribution
Graduated circle
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What type of map is this?
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What type of map?
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What type of map?
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What type of map?
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What is qualitative vs. quantitative
qualities?
• Qualitative: shows the distribution of a
particular set of information; ex. map
showing the distribution of U.S. national
parks
• Quantitative: show spatial characteristics
of numerical data; ex. map showing
population of California
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What are mental maps?
• Individual’s internal geographic
understanding of a place (aka cognitive
map)
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What is a cartogram?
• A presentation of statistical data in
geographical distribution on a map
This cartogram shows world
population that is why China
and India are more larger than
the other nations…
Cartograms exaggerate sizes
based on statistical value of
particular theme represented in
map