# Chapter 2: Portraying Earth

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Chapter 2: Portraying Earth

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 Maps are always smaller than the area they represent
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 Large vs. small map scales Large scale Small 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 Title Date Legend Scale Direction Location
Figure 2-5 Title Date Legend Scale Direction Location Data Source Map Projection

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 Cartography: construction & production of maps
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 Many types Lines that join points of equal value
Isobar: line of constant pressure Isotherm: line of constant temperature Isohyet: line of constant precipitation Figure 2-16

Isolines 800 600 500 700 400 300

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 “active” satellites Several older backup satellites Wide Area Augmentation System (WAAS) Continuously Operating GPS Reference Stations (CORS) Figure 2-19

Aerial Photography—Figure 2-20
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 Sonar Imagery Thermal IR scanning
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

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 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.”