Chapter 2: Portraying Earth

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Chapter 2: Portraying Earth
McKnight’s Physical Geography:
A Landscape Appreciation,
Portraying Earth
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The Nature of Maps
Map Scale
Map Essentials
The Role of Globes
Map Projections
Families of Map Projections
Isolines
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Portraying Earth
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•
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GPS—Global Positioning System
Remote Sensing
GIS—Geographic Information Systems
Tools of the Geographer
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The Nature of Maps
• 2-dimensional
representation of
Earth’s surface
• Show 4 key properties
of a region
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–
–
–
Size
Shape
Distance
Direction
Figure 2-2b
• Maps are imperfect, since
Earth is a sphere
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Map Scale
• Maps are always smaller than
the area they represent
• Map scales are necessary to
understand realistic distances
on map
• Scale is relationship between
area on map and area on
Earth
• Three primary types
Figure 2-3
– Graphic
– Fractional
– Verbal
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Map Scale
• Large versus small map scales
Map Essentials
• Need several properties
of maps to help with
interpretation:
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–
–
–
–
–
–
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Title
Date
Legend
Scale
Direction
Location
Data Source
Map Projection
Figure 2-5
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The Role of Globes
• Advantages of Globes
– Maintains correct geographic
relationships between points
– Can accurately represent spatial
relationships between points on
Earth
• Disadvantages of Globes
– Only can see a hemisphere at a
time
– Large and bulky
– Cannot contain much detail
Figure 2-6
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Globe properties

Parallels of latitude
 parallel to each other
 decrease in length closer to
the poles

Meridians of longitude
 converge at the poles
 equal length (1/2 equator)
•
Both: intersect at right
angles
Map Projections
A.
B.
C.
D.
Process of transferring the spherical earth onto a
2-dimensional surface.
Estimate size and shape of earth in 3 dimensions
Properties of map projections:
 equal area (area)
 conformal (shape)
 equidistant (distance)
 azimuthal (direction)
Types of map projections:
 cylindrical
 conic
 azimuthal (planar)
Map Projections
• Equivalence versus conformality dilemma
Figure 2-10
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Families of Map Projections
• Cylindrical Projections
– “Wrap” the globe in a
cylinder of paper
– Paper tangent to Earth
at equator
– Conformal projection
– Mercator projection is
most famous
Figure 2-7
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Map Projections
Mercator projection
Transverse Mercator
Families of Map Projections
• Plane Projections
– Project globe onto a
paper that is tangent to
globe at some point
– Displays one
hemisphere well
– Equivalent projection
– An example is an
orthographic plane
projection (Figure 2-13)
Figure 2-9
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Families of Map Projections
• Conic Projections
– Project the map onto a
cone tangent to or
intersecting the globe
– Principal parallel
– Good for mapping
small areas on Earth
– Impractical for global
mapping
Figure 2-8
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Families of Map Projections
• Pseudocylindrical
Projections
– A mix of conformal and
equivalent
– Central parallel and
meridian cross at right
angles
– Oval shaped; distortion
increases as you move
away from the center
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Figure 2-11
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Families of Map Projections
• Interrupted Projections
– Minimize distortion
– Discontinuous map,
shapes and sizes
maintained
– Typically oceans are
distorted; land masses
maintain original
shape and size
– Goode’s projection
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Figure 2-14
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Isolines
• Definition
• Many types
– Isobar: line of constant
pressure
– Isotherm: line of constant
temperature
– Isohyet: line of constant rain
– Isoamplitude: line of
constant wave amplitude
• Construction steps/rules
Figure 2-16
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Isolines
800
700
600
500
400
300
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Isolines
• Topographic Maps
– Show elevation
contours
– Contour lines
– Lines closer together
represent steeper
terrain
– Often used in
geography
Figure 2-15
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Isolines
• Topographic Maps
– Show elevation
contours
– Lines closer together
represent steeper
terrain
– Often used in
geography
Figure 2-15
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GPS—Global Positioning System
• Global navigation satellite
system for determining
location on Earth’s
surface
• Wide Area Augmentation
System (WAAS)
• Continuously Operating
GPS Reference Stations
(CORS)
Figure 2-19
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Imagine you are somewhere in the United
States and you are TOTALLY lost -- for
whatever reason, you have absolutely no
clue where you are.
You find a friendly local and ask, "Where
am I?" He says, "You are 625 miles from
Boise, Idaho."
This is a nice, hard fact, but it is not
particularly useful by itself. You could be
anywhere on a circle around Boise that has
a radius of 625 miles, like this:
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You ask somebody else where you
are, and she says, "You are 690
miles from Minneapolis, Minnesota."
Now you're getting somewhere. If
you combine this information with
the Boise information, you have two
circles that intersect.
You now know that you must be at
one of these two intersection points,
if you are 625 miles from Boise and
690 miles from Minneapolis.
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If a third person tells you that you
are 615 miles from Tucson, Arizona,
you can eliminate one of the
possibilities, because the third circle
will only intersect with one of these
points. You now know exactly where
you are -- Denver, Colorado.
This same concept works in threedimensional space, as well, but
you're dealing with spheres instead
of circles.
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Remote Sensing
• Measurement by a device
not in contact with Earth’s
surface
• Common types include:
– Aerial Photographs
– Orthophoto maps
– Visible Light and Infrared
(IR) Scanning
– Thermal IR scanning
– Radar and Sonar
– Many others
Aerial Photography—Figure 2-20
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Remote Sensing
• Orthophoto maps
– Photographic maps that
are multicolored and
distortion free
– Useful in low-lying coastal
regions to show marsh
topography
Figure 2-21
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Remote Sensing
• Visible light and IR
scanning
– Based off of visible light and
IR part of electromagnetic
spectrum (Figure 2-22)
– Shows “false color”
Figure 2-23
Figure 2-22
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Remote Sensing
• Radar Imagery
– “Radio Detection and Ranging”
– Useful for identifying atmospheric moisture
• Sonar Imagery
– “Sound Navigation and Ranging”
– Permits underwater imaging
• Thermal IR scanning
– Scans in the thermal IR part of spectrum
– Shows images based on temperature
– Often utilized in meteorology
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GIS—Geographic Information
Systems
• Computer systems used to
analyze and display spatial
data
• Layers of data used in
mapping
• Requires high powered
computing to process
multiple maps
Figure 2-29
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Tools of the Geographer
• Vast array of maps, remotely sensed satellite
imagery, and computer applications
• Difficult to determine the best way to use all of
this information
• Some tools better at identifying features on
Earth than others
• Ultimate goal: “To better understand Earth.”
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Summary
• Maps are essential to portray features on Earth’s
surface
• Need a map scale to identify how a map relates
to the actual surface features on Earth
• Many other map properties are essential to
interpreting a map
• Globes have several advantages and
disadvantages
• Representing Earth in 2 dimensions can be done
through map projections
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Summary
• Many different map projections exist
• Dilemma of equivalent versus conformal
• Plotting isolines on a map can help with
interpretation of features on the map
• The global positioning system (GPS) helps to
identify location on Earth’s surface
• Remote sensing is a measurement of Earth’s
surface from a system not on Earth’s surface
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Summary
• Many different remote sensing instruments
exist, including satellite, radar, and sonar
• GIS are computer systems used to analyze and
display spatial data, often in layers
• The geographer has many tools, but the
ultimate goal is “To better understand Earth.”
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