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Chapter 2: Portraying Earth
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  1. Chapter 2: Portraying Earth

  2. What’s Your Perspective?

  3. Ptolomy’s “World” Map circa 150 A.D.

  4. World Maps from the 1500’s

  5. 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

  6. 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

  7. 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. 8 Map Essentials Figure 2-5 • Title • Date • Legend • Scale • Direction • Location • Data Source • Map Projection

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. Isolines 700 600 500 800 400 300

  19. 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

  20. 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

  21. 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

  22. Stereoscopy Uses overlapping vertical photographs Requires 2 vertical aerial photographs that align & overlap at least 60% Produces 3-D appearance Remote Sensing Figure 2-A (a & b)

  23. 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

  24. 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

  25. 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

  26. GIS—Geographic Information Systems Figure 2-29 • Computer systems used to store, analyze and display spatial data • Use layers of data for mapping

  27. 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-bk-eargen&utm_term=google%20earth

  28. 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.”

  29. 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 • 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.”