Chapter 2: Portraying Earth

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Chapter 2: Portraying Earth
What’s Your Perspective?
2
Ptolomy’s “World” Map circa
150 A.D.
World
Maps
from the
1500’s
The Nature of Maps
• Geographical illustration
• 2-D representation of Earth’s surface
• Show 4 key properties:
– Size
– Shape
– Distance
– Direction
• All maps are imperfect,
since Earth is a sphere
• Mental maps
Figure 2-2b
Map Scale
Figure 2-3
• Maps are always smaller than
the area they represent
• Scale is the relationship
between area on map to same
area on Earth
• 3 types
– Fractional
• Ratio or fraction to compare
map distance to Earth
distance
– Graphic
• Line marked off with distances
– Verbal
• Words tell ratio of map distance
to Earth distance
Figure 2-4
Map Scale
Figure 2-4
• Large vs. small
map scales
• Large scale
– Large
representative
fraction (small
denominator)
– Shows smaller
area, but with
more details
• Small scale
– Small
representative
fraction (large
denominator)
– Shows larger
area, but with
less details
8 Map Essentials
Figure 2-5
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Title
Date
Legend
Scale
Direction
Location
Data Source
Map
Projection
The Role of Globes
• Advantages of Globes
– Maintains correct geographic
relationships between points
– Accurately represents spatial
relationships between points on
Earth
– Essentially, no distortion
• Disadvantages of Globes
– Only can see 1 hemisphere
(half) at a time
– Large and bulky
– Cannot contain much detail
Figure 2-6
Map Projections
Figure 2-2d
• Cartography: construction &
production of maps
– Cartographer: a person who makes
maps
• Challenge:
– Combine geographic exactness of
globe with convenience of flat map
– Fundamental Problem: minimize
distortion while transferring from a
rounded to a flat surface
• Definition of map projection
– System to transform a
curved surface to a flat
display
Map Projections
• 2 primary types
– Equivalent—ratio of areal size on map & Earth is the same
• Distorts shapes
– Conformal—location shape on the map is the same as on Earth
• Distorts sizes
Figure 2-10
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
• Invented over 400 years
ago for ocean navigation
• Distortion increases as
you move poleward
• Latitudes spaced farther
apart poleward to minimize distortion
Figure 2-7
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
Figure 2-9
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
Families of Map Projections
• Pseudocylindrical Projections
– Mix of conformal and equivalent
– Central parallel and meridian cross at right angles
– Oval shaped; distortion increases as you move away from the
center
Figure 2-11
Families of Map Projections
• Interrupted Projections
– Minimize distortion on continents
– Discontinuous map, shapes and sizes maintained
– Typically oceans are distorted; land masses maintain original
shape and size
Figure 2-14
Isolines
• Definition
– Lines that join points of equal
value
• Many types
– Isobar: line of constant
pressure
– Isotherm: line of constant
temperature
– Isohyet: line of constant
precipitation
Figure 2-16
Isolines
800
700
600
500
400
300
Isolines
Figure 2-15
• Rules:
– Always closed lines (no ends)
– Show gradations in quantities
– Lines do not cross
• Interval: numeric difference
between individual isolines
• Index contour: usually every 4th
or 5th line is bolder & marked
with that line’s elevation
– Used to calculate intervals
• Topographic Maps
– Contour lines: lines connecting
points of equal elevation
– Lines closer together represent
steeper terrain
GPS—Global Positioning System
• Global navigation satellite system for determining location
on Earth’s surface
– Network of 24-30 “active” satellites
– Several older backup satellites
• Wide Area Augmentation System
(WAAS)
• Continuously Operating
GPS Reference Stations
(CORS)
Figure 2-19
Remote Sensing
• Measurement by a device not in contact with Earth’s
surface (balloon, airplane, rocket, satellite)
• Common types include:
– Aerial Photographs
• 1st form of remote sensing
– Oblique: camera angle less than 90°
– Vertical: camera angle perpendicular to Earth’s surface
– Photogrammetry:
science of mapping
from aerial
photographs
– NASA Connect
Remote Sensing
Aerial Photography—Figure 2-20
Remote Sensing
• Stereoscopy
– Uses overlapping vertical
photographs
• Requires 2 vertical aerial photographs
that align & overlap at least 60%
• Produces 3-D
appearance
Figure 2-A (a & b)
Remote Sensing
• Orthophoto maps
– Photographic maps that are multicolored & distortion free
• Precise distance measurements
– Useful in low-lying
coastal regions
to show marsh
topography
Figure 2-21
Remote Sensing
• Visible light & 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
Remote Sensing
• Radar Imagery
– Helps identify atmospheric moisture
• Sonar Imagery
– Permits underwater imaging
• Thermal IR scanning
– Scans in thermal IR part of spectrum
– Shows images based on temperature
GIS—Geographic Information
Systems
Figure 2-29
• Computer systems used to
store, analyze and display
spatial data
• Use layers of data for
mapping
GIS—Geographic Information
Systems
• Google Maps
– http://maps.google.com/
• Sarpy County Internet Mapping Service
– http://maps.sarpy.com/sims20/
• Douglas-Omaha GIS
– http://www.dcgis.org/dogis/
• Google Earth
– http://www.google.com/earth/
index.html#utm_campaign=
en&utm_medium=ha&utm_
source=en-ha-na-us-bkeargen&utm_term=
google%20earth
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
• Computer Technology
– Improved speed and
data handling
– Greatly reduced time in
producing maps
– Allows cartographers to
examine different map
layouts
• Ultimate goal: “To better understand Earth.”
Summary
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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
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
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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