chapter 2: portraying earth mcknight’s physical geography: a landscape appreciation,

Chapter 2: Portraying Earth

McKnight’s Physical Geography: A Landscape Appreciation,

Portraying Earth

• 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

• 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– Size– Shape– Distance– Direction

• Maps are imperfect, since Earth is a sphere

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Figure 2-2b

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– Graphic

– Fractional

– Verbal

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Figure 2-3

Map Scale• Large versus small map scales

Map Essentials

• Need several properties of maps to help with interpretation:– Title– Date– Legend– Scale– Direction– Location– Data Source– Map Projection

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Figure 2-5

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

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Figure 2-6

Globe Globe propertiesproperties

ParallelsParallels of latitude parallel to each other decrease in length closer

to the poles MeridiansMeridians of longitude

converge at the poles equal length (1/2 equator)

• Both: intersect at right angles

Map Projections

A. Process of transferring the spherical earth onto a 2-dimensional surface.

B. Estimate size and shape of earth in 3 dimensionsC. Properties of map projections:

equal area (area) conformal (shape) equidistant (distance) azimuthal (direction)

D. Types of map projections: cylindrical conic azimuthal (planar)

Map Projections• Equivalence versus conformality dilemma

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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

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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)

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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

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Figure 2-8

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

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

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

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Figure 2-16

Isolines

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800

700600 500 400

300

Isolines

• Topographic Maps– Show elevation

contours– Contour lines– Lines closer together

represent steeper terrain

– Often used in geography

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Figure 2-15

Isolines

• Topographic Maps– Show elevation

contours– Lines closer together

represent steeper terrain

– Often used in geography

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Figure 2-15

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)

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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 three-dimensional space, as well, but you're dealing with spheres instead of circles.

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

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Aerial Photography—Figure 2-20

Remote Sensing

• Orthophoto maps– Photographic maps that

are multicolored and distortion free

– Useful in low-lying coastal regions to show marsh topography

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Figure 2-21

Remote Sensing

• Visible light and IR scanning– Based off of visible light and

IR part of electromagnetic spectrum (Figure 2-22)

– Shows “false color”

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Figure 2-23Figure 2-22

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

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Figure 2-29

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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