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Cartography: the science of map making


... the earth in half and each half is known as a hemisphere. 2) are the circumference of the earth. 3) provide the shortest routes of travel on the earth's surface. ... – PowerPoint PPT presentation

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Title: Cartography: the science of map making

Cartography the science of map making
Locating yourself on a Globe
  • You need a frame of reference
  • That is the purpose of Latitude and Longitude
  • Defining these parameters
  • Earth rotates on an imaginary axis North and
    South Poles
  • Equator is a great circle that lies equidistant
    between them.

Great Circles
  • ..are imaginary circles of the surface of the
    earth who's plane passes through the center of
    the earth.
  • The circumference of the earth is 25,000 miles of
    40,000 km
  • "Great" because it is the largest possible

Great Circles
  • 1) cut the earth in half and each half is known
    as a hemisphere
  • 2) are the circumference of the earth
  • 3) provide the shortest routes of travel on the
    earth's surface.
  • Planes travel in great circles.
  • We were always taught a line is the shortest
    distance between two points - Not True.
  • Small circles circles whose planes do not pass
    through the center of the earth.

  • Latitude is the angular distance north or south
    of the equator.
  • 1 of latitude 112 km 360/40,000 km
  • 1 degree 60 minutes
  • 1 minute 60 seconds 3649'52" N
  • ArcView uses Decimal Degrees
  • Sextant measures the angular distance between 2
    points (sun horizon)
  • So it easy to determine latitude.

  • Longitude no natural reference point
  • In 1884 by International Agreement Greenwich
    England was the chosen starting point.
  • This is called the prime meridian or zero degrees
    and everything is east or west of that.
  • (angular distance from Greenwich, England)

The global grid
  • Parallels lines of latitude, only the equator is
    a great circle all other parallels are small
    circles (they never meet)
  • Meridians these are line of longitude and when
    joined with its mate half way around the globe
    form great circles
  • the distance between meridians will vary with

Global Coordinate System
  • Longitude and Latitude
  • Degrees, minutes, seconds
  • 1o latitude 110.5 km (equator)
  • 1o longitude 111.3 cos(latitude)
  • Meridian
  • Parallel
  • Great and Small Circles

How the Earth is Divided
  • Hemispheres Northern, Southern, Eastern,

Time Zones
  • Solar noon most towns used this, defined as when
    a vertical stake cast the shortest shadow.
  • By the 19th century transportation and
    communications (namely railroads and telegraph)
    connected towns and cities, the adopt of a
    standard time was necessary.

Time Zones (continued)
  • 1884 at the International Meridian Conference 24
    time zones were established.
  • Greenwich Mean Time (GMT) Universal time
    Zulu time
  • 360/24 15 for each time zone, however for
    convenience many time zones follow state and
    country lines.
  • International Date Line where each new day
    begins 180th meridian
  • Chronometer

Time Zones

  • The Globe is a nearly perfect representation of
    the earth, it shows the shape and spatial
    relationships of land and water.
  • Problem Can only look at 1/2 at a time.
  • However globes can not show detail and are big
    and clumsy.

Benefits of Maps
  • Maps are the geographers most important tool.
  • Benefits
  • reproduced easily and inexpensive
  • different scales
  • can put an enormous amount of information on a
  • roads, buildings, property lines, vegetation,
  • distribution of land forms

Map Features important in GIS
  • Areas
  • Lines
  • width exaggeration
  • Points
  • size exaggeration

On a globe four properties are true
  • 1) parallels of latitude are always parallel
  • 2) parallels are evenly spaced
  • 3) meridians of longitude converge at the poles
  • 4) meridians and parallels cross everywhere at
    right angles

Map Projection
  • A map projection is a mathematical formula for
    representing the curved surface of the earth on a
    flat map.

Think of a light bulb
  • distance
  • area
  • shape
  • direction

You must make a choice between
  • Equivalence equal area relationship throughout
    the map, however you get distorted shapes.
  • Conformal shapes are true and meridians and
    parallels are at right angles, however land
    masses are greatly enlarged at high latitudes.
  • Except for very small areas Conformality and
    Equivalence are mutually exclusive.
  • There are over 1000 different projections.

Other types of considerations
  • Equidistant projections However scale is not
    maintained correctly by any projection throughout
    an entire map
  • True-direction projections or azimuthal
    projections, maintain some of the great circle
    arcs. (The shortest distance between 2 points on
    a globe is the great circle route.)

Map Projection
  • Distortions are inherent in maps
  • Earth is round, map is flat
  • Projection is the term used to describe the
    process of mapping a round surface to flat paper
  • wide variety of projections possible
  • each projection causes different distortions to

Map Projections Types
Cylindrical Projection example Mercator
  • Tangent to the globe at the equator. No
    distortions at the equator but it increases
    moving North or South. Nice rectangular grid.
  • Why are they used in Navigation?
  • A straight line drawn anywhere on a Mercator
    projection is a true compass heading this is
    called a rhumb line.
  • However, the distance along this line may vary.

Variations on Cylindrical Projection
Azimuthal Projection example Many Polar
  • Plane is tangent to the globe at some point N or
    S of the equator or one point on the equator. No
    distortion at the point of tangency but it
    increases moving away. All directions from the
    center are accurate. It is like a view from
    space. Can only see half the world at once.
  • All great circles passing through the point of
    tangency appear as straight lines.
  • Good for knowing the great circle path (I.e.
    shortest distances, important to navigators.

Variations of Azimuthal Projections
Conic exampleLambert Conformal Conic
  • One or more cones tangent to one or more
    parallels. Best for mid-latitudes in an E-W
    direction (U.S.)
  • A straight line is almost a perfect great circle
    route (planes use this)
  • Can be conformal or equivalent

Variations on conic projections
  • The conversion between projections involving
    mathematical formulas.
  • Good GIS packages can do this.
  • Overlaying different projections is not possible.

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