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Chapter Two Portraying Earth

Physical Geography
by

Lisa Schmidt

on 29 January 2014

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Transcript of Chapter Two Portraying Earth

McKnight’s Physical Geography: A Landscape Appreciation, Tenth Edition, Hess
GPS—Global Positioning System
Remote Sensing
GIS—Geographic Information Systems
Tools of the Geographer
Portraying Earth
Chapter 2: Portraying Earth
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
Summary
Figure 2-29
Computer systems used to analyze and display spatial data
Layers of data used in mapping
Requires high powered computing to process multiple maps
GIS—Geographic Information Systems
Figure 2-21
Orthophoto maps
Photographic maps that are multicolored and distortion free
Useful in low-lying coastal regions to show marsh topography
Remote Sensing
Figure 2-19
GPS—Global Positioning System
Figure 2-16
Isolines
Figure 2-11
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
Families of Map Projections
Figure 2-9
Plane Projections
Project globe onto a paper that is tangent to globe at some point
Displays one hemisphere well
Equivalent projection
Families of Map Projections
Figure 2-10
Equivalence versus conformality dilemma
Map Projections
Challenge of the cartographer (“mapmaker”)
Combine geographic exactness of globe with convenience of flat map

Two primary types
Equivalent—ratio of areal size on map and Earth is the same
Conformal—shape of locations on the map is the same as on Earth
Map Projections
Figure 2-6
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
The Role of Globes
Figure 2-4
Large versus small map scales
Map Scale
Figure 2-3
Three primary types
Graphic
Fractional
Verbal
Map Scale
The Nature of Maps
Map Scale
Map Essentials
The Role of Globes
Map Projections
Families of Map Projections
Isolines
Portraying Earth
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.”
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
Summary
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.”
Tools of the Geographer
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
Remote Sensing
Figure 2-22
Figure 2-23
Visible light and IR scanning
Based off of visible light and IR part of electromagnetic spectrum (Figure 2-22)
Shows “false color”
Remote Sensing
Figure 2-14
Interrupted Projections
Minimize distortion
Discontinuous map, shapes and sizes maintained
Typically oceans are distorted; land masses maintain original shape and size
Goode’s projection
Families of Map Projections
Figure 2-8
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
Families of Map Projections
Figure 2-7
Cylindrical Projections
“Wrap” the globe in a cylinder of paper
Paper tangent to Earth at equator
Conformal projection
Mercator projection is most famous
Families of Map Projections
Figure 2-5
Need several properties of maps to help with interpretation:

Title
Date
Legend
Scale
Direction
Location
Data Source
Map Projection
Map Essentials
Figure 2-2b
The Nature of Maps
Aerial Photography—Figure 2-20
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
Remote Sensing
Isolines
aerial photograph
conformality (conformal projection)
conic projection
cylindrical projection
elevation contour line
equal area projection
equivalence (equivalent projection)
fractional scale
geographic information systems (GIS)
orthophoto map
photogrammetry
plane projection
pseudocylindrical projection(elliptical projection)
radar
remote sensing
representative fraction
rhumb line
small-scale map
sonar
verbal scale
global positioning system (GPS)
graphic scale
isoline
large-scale map
loxodrome
map
map projection
map scale
Mercator projection
multispectral scanning system (MSS)
Chapter Two Vocabulary
Chapter Outline
Map—a two-dimensional representation of the spatial distribution of selected phenomena.
Show 4 key properties of a region
Size
Shape
Distance
Direction

Maps are imperfect, since Earth is a sphere
Their ability to show distance, direction, size, and shape in horizontal (two-dimensional) spatial relationships makes them indispensable.

They depict graphically what is where and they are often helpful in providing clues as to why such a distribution occurs.
Basic fault of maps:
No map can be perfectly accurate:
Maps are trying to portray the impossible—taking a curved surface and drawing it on a flat piece of paper.
Map Scale
—gives the relationship between length measured on the map and corresponding distance on the ground. Essential for being able to measure distance, determine area, and compare sizes.
Scale can never be perfectly accurate, again because of the curve of Earth’s surface.
The smaller the area being mapped, the more accurate the scale can be.
Graphic Map Scales
Uses a line marked off in graduated distances; remains correct when map is reproduced in another size, because both the graphic scale line and the map size change in same dimension.
Fractional Map Scales

Uses a ratio or fraction, called a representative fraction, to express the comparison of map distance with ground distance on Earth’s surface.

1/63,360 is commonly used because the number in denominator equals the number of inches in one mile.

Often, no units are given in a fractional scale, so the dimensions translate whether one is using inches, millimeters, or some other unit of measurement.
Verbal Map Scales
Also called word scale; uses words to give the ratio of the map scale length to the distance on Earth’s surface.
Large-scale map
—has a relatively large representative fraction, which means the denominator is “small”—1/10,000 is large-scale as compared to 1/1,000,000.

Portrays only a small portion of Earth’s surface, providing considerable detail.

Small-scale map
—has a small representation fraction, which means the denominator is “large.”

Portrays a larger portion of Earth’s surface, but gives only limited detail.
Maps should include a few essential components; omitting any of these components will decrease the clarity of the map and make it more difficult to read.
The eight essential components are Title, Date, Legend, Scale, Direction, Location, Data Source, and Projection Type.
Title—should provide a brief summary of the map’s content or purpose and identify the area it covers.
Date—should indicate the time span in which the map’s data were collected.
Legend—should explain any symbols used in the map to represent features and any quantities.
Scale—should provide a graphic, verbal, or fractional scale to indicate the relationship between length measured on the map and corresponding distance on the ground.
Direction—should show direction either through geographic grid or a north arrow.
Location—should have a grid system, either a geographic grid using latitude and longitude, or an alternative system that is expressed like the x and y coordinates of a graph.
Data Source—should indicate the data source for thematic maps.
Projection type—should indicate the type of projection, particularly for small-scale maps.
Map projection—the system used to transform the rounded surface of Earth to a flat display.
A map which portrays shape accurately is called a conformal map. Conformal maps are useful in that they help us understand the true shape of the items on the map. However, these maps have
many drawbacks. A conformal map tends to get quite distorted, especially towards the top and bottom of the map. This creates problems with scale. The scale may be accurate near the equator,
but the further one travels form the equator, the less accurate the scale becomes.
Impossible to perfectly portray both size and shape, so must strike a compromise between equivalence and conformality.
Mercator: The Most Famous Projection
The Mercator projection—a special-purpose projection that was created more than 400 years ago as a tool for straight-line navigation

Greenland appears much larger than Africa, South America, and Australia, although Greenland is actually smaller than them.
Indeed, Africa is 14 times larger than Greenland.
How do navigators use Mercator projection?
First, navigators must use another type of projection that shows great circles as straight lines; they draw a straight line between their starting point and destination.
They then transfer that straight-line route to a Mercator projection by marking spots on the meridians where the straight-line route crossed them.
They then draw straight lines between the meridian points, which are loxodromes or rhumb lines.
The navigator can use these loxodromes to chart when periodic changes in compass course are necessary to approximate the shortest distance between two points.
Distortion increases with distance from this circle. As such, conic projections are best used with landmasses possessing great east–west orientations.
Because of the distortion associated with them, they are better suited for mapping smaller regions (i.e., a single country).
Isoline—commonly used cartographic device for portraying the spatial distribution of some phenomenon. Also called isarithm, isogram, isopleth, and isometric line.
Refers to any line that joins points of equal value.
Elevation contour line—joins points of equal elevation
Isotherm—joins points of equal temperature
Isobar—joins points of equal atmospheric pressure
Isohyet—joins points of equal quantities of precipitation
Isogonic line—joins points of equal magnetic declination
Isolines help to reveal spatial relationships that otherwise might go undetected.
They can significantly clarify patterns that are too large, too abstract, or too detailed for ordinary comprehension.
Basic characteristics of isolines:
They are always closed lines, having no ends;
They represent gradations in quantities, so only touch or cross one another in very rare and unusual circumstances;
Interval—the numerical difference between one isoline and the next;
Size of interval is up to the cartographer’s discretion, but it is best to maintain a constant interval thorough a map;
Their proximity depends on the gradient (that is, the change in the interval).
The closer they lie together, the steeper the gradient; the further apart they lie, the more gentle the gradient.
Global Positioning System (GPS)
—a satellite-based system for determining accurate positions on or near Earth’s surface.
High-altitude satellites (24) continuously transmit both identification and position information that can be picked up by receivers on Earth. Clocks stored in both units help in calculating the distance between the receiver and each member of a group of four (or more) satellites, so one can then determine the three-dimensional coordinates of the receiver’s position.
Military units allow a position calculation within about 30 feet (10 meters).
Also used in earthquake prediction, ocean floor mapping, volcano monitoring, and mapping projects.
Because of accuracy of GPS units, latitude and longitude are increasingly being reported in decimal form.
Aerial photograph—photograph taken from an elevated “platform” such as a balloon, airplane, rocket, or satellite.
Aerial Photographs were the first form of remote sensing
Photogrammetry—science of obtaining reliable measurements from photographs and, by extension, the science of mapping from aerial photographs
Show the landscape in much greater detail than a conventional map, but are like a map in that they provide a common scale that allows precise measurement of distances
Color infrared (color IR)—refers to the infrared region of the spectrum. Color IR film is more versatile; uses include evaluating health of crops and trees.
Thermal scanning is used for showing diurnal temperature differences between land and water and between bedrock and alluvium, for studying thermal water pollution, for detecting forest fires, and, its greatest use, for weather forecasting.
Radar—(radio detection and ranging) senses wavelengths longer than 1 millimeter and now provides images in photo-like form.
Radar is unique in its ability to penetrate atmospheric moisture, so it can analyze wet tropical areas that can’t be sensed by other systems.
Radar is particularly useful for terrain analysis.
Sonar—(sound navigation ranging) permits underwater imaging.
Geographic information systems (GIS)—automated systems for the capture, storage, retrieval, analysis, and display of spatial data.
Uses both computer hardware and software to analyze geographic location and handle spatial data.
Virtually, libraries of information that use maps instead of alphabet to organize and store data.
Allows data management by linking tabular data and map.
Mainly used in overlay analysis, where two or more layers of data are superimposed or integrated.
First uses were in surveying, photogrammetry, computer cartography, spatial statistics, and remote sensing; now being used in all forms of geographic analysis, and bringing a new and more complete perspective to resource management, environmental monitoring, and environmental site assessment.
GIS was also used to compile structural data on the rubble at Ground Zero at the World Trade Center disaster.
The technology allowed the building damage to be mapped and provided details on the outage of various utilities in the area.
Reminder
Ch 2 quiz opens after class.
Chapter Outline
Full transcript