CARTOGRAPHIC BASICS

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COMMON MAP PROJECTIONS

• Equal Area Projections
• Property of equal area commands high priority
  on
• most maps used as small scale general
  reference
• maps and for instruction
• Choice of equal area projection depends on
  these
• two considerations
• Size of the region to be mapped
• Distribution of the angular deformation (shape
• considerations)

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COMMON MAP PROJECTIONS Equal Area
Figure 5.B.4 A few of the many equivalent world
map projections. (A) cylindrical equal-area with
standard parallels at 30 N and S latitude (B)
sinusoidal projection and (C) Mollweides
projection. The black lines are values of 2O.
From Robinson, Sixth Edition, page 72
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COMMON MAP PROJECTIONS Equal Area

• Albers
• Conic projection with two standard parallels
• Any two small circles, reasonably close
  together are
• used
• Low distortion, especially along parallels
• Resembles earths graticule curved
  parallels,
• converging meridians
• Best for mid-latitude areas with greater
  east-west
• extension than north-south
• Standard for many US Government base maps,
• including Census Bureau

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COMMON MAP PROJECTIONS Equal Area Albers
From Robinson, Sixth Edition, page 81
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COMMON MAP PROJECTIONS Equal Area

• Lamberts
• Azimuthal as well as equivalent
• Distortion symmetrical around a single point
• Point can be located anywhere on globe
• Good for areas that have nearly equal
  east-west vs.
• north-south extension, such as some
  individual
• states

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COMMON MAP PROJECTIONS Equal Area

• Cylindrical
• Two standard parallels which may coincide at
  the
• equator, but otherwise must be
  homolatitudes
• Distortion arranged parallel to standard small
  circles
• When parallels are chosen at 30, this
  projection
• provides the least overall mean angular
  distortion of
• any equal area world projection

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COMMON MAP PROJECTIONS Equal Area

• Sinusoidal
• Conventionally has straight central meridian
  and
• equator no angular distortion along either
• Illusion of proper spacing useful when
  latitudinal
• relations are important
• Particularly suitable, when properly centered,
  for maps
• of less-than-world areas - - - South America

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COMMON MAP PROJECTIONS Equal Area - Sinusoidal
From Robinson, Sixth Edition, page 68
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COMMON MAP PROJECTIONS Equal Area

• Mollweids
• Appears more realistic than sinusoidal
• North-south decreased in high latitudes and
  increased
• in mid-latitudes
• East-west scale increased in high latitudes
  and
• decreased in mid-latitudes
• Two areas of least distortion are in the
  mid-latitudes,
• so projection is most useful for those areas

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COMMON MAP PROJECTIONS Equal Area

• Goodes Homolosine
• Combines equatorial section of sinusoidal and
  poleward
• sections of Mollweids
• Must be constructed from the same area scale
  (ie.
• reference globe)
• Sinusoidal and Mollweids have one parallel of
  identical
• length along which they may be joined
• Usually used in interrupted form
• Popular in the United States

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COMMON MAP PROJECTIONS Equal Area Goodes
Homolosine
From Robinson, Sixth Edition, page 81
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COMMON MAP PROJECTIONS

• Azimuthal Projections (preserve direction)
• Projected on a plane that centered anywhere on
  the
• reference globe
• Line perpendicular to plane passes through
  center of
• globe
• Distortion is symmetrical around the center
  point
• peripheral distortion is extreme
• All great circles passing through the central
  point
• show as straight lines with the correct
  azimuth

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COMMON MAP PROJECTIONS Azimuthal

• Azimuthal Equidistant
• Has linear scale, uniform along radiating
  straight
• lines through center
• Movement toward or away from a center point is
  well
• demonstrated
• Works well for mapping radio impulses or
  seismic
• waves

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COMMON MAP PROJECTIONS Azimuthal Equidistant
From Robinson, Sixth Edition, page 85
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COMMON MAP PROJECTIONS Azimuthal

• Orthographic
• Looks something like a perspective view of the
  globe
• from a distance
• Distortion is less visually obvious than on
  other
• azimuthal projections
• Useful for illustrations which portray the
  globe as a
• sphere

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COMMON MAP PROJECTIONS Azimuthal

• Gnomic
• All great circle arcs are straight lines
  everywhere on
• the projection
• Useful primarily for marine navigation

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COMMON MAP PROJECTIONS Azimuthal
Stereographic Lamberts Equal Area Azimuthal Equ
idistant Orthographic Gnomic
From Robinson, Sixth Edition, page 84
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COMMON MAP PROJECTIONS

• Special Purpose Map Projections
• Plane chart/equidistant cylindrical/PlateCarrée
  /
• equirectangular
• Oldest and simplest map projection
• Used for navigation before Mercator
• Good for city maps and base maps of
• small areas
• Simple conic
• Uses two standard parallels equidistant
  from
• equator
• No great distortion of angles or areas
• Often used in atlases for mid-latitude areas

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COMMON MAP PROJECTIONS Special Purpose
Equidistant Cylindrical/Plane Chart
From Robinson, Sixth Edition, page 86
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COMMON MAP PROJECTIONS Special Purpose Simple
Conic
From Robinson, Sixth Edition, page 87
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COMMON MAP PROJECTIONS

• Special Purpose Map Projections, cont.
• Polyconic not conformal or equal area
• Used by the U.S. for topo sheets until 1950s
  can fit
• topos together in one direction or another, but
  not all
• Robinsons not conformal or equal area
• Commissioned in 1961 by Rand McNally to show
• uninterrupted world maps at all scales
• Minimizes the appearance of shape and area
• distortion

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COMMON MAP PROJECTIONS Special Purpose -
Polyconic
The distribution of scale factors on a polyconic
projection in the vacinity of 40 latitude. N-S
SF values away from the central meridian are
approximate. Note that the section of the
projection which is used for a standard
7.5-minute quadrangle map would be 1/8 degree E-W
and N-S along the central meridian.
From Robinson, Sixth Edition, page 88, 89
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COMMON MAP PROJECTIONS

• Special Purpose Map Projections, cont.
• Space Oblique Mercator Projection
• Projection used for satellite imagery
• Essentially conformal (shape/angle)
• Groundtrack of satellite represents central line
  with
• scale factor 1.0
• Groundtrack is not true great circle, but
  slightly
• curved due to rotation of earth

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COMMON MAP PROJECTIONS Special Purpose
Space Oblique Mercator
Robinsons