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CARTOGRAPHIC BASICS

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... less-than-world areas - - - South America. COMMON MAP PROJECTIONS. Equal ... uninterrupted world maps at all scales. Minimizes the appearance of shape and area ... – PowerPoint PPT presentation

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Title: CARTOGRAPHIC BASICS


1
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)

2
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
3
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

4
COMMON MAP PROJECTIONS Equal Area Albers
From Robinson, Sixth Edition, page 81
5
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

6
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

7
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

8
COMMON MAP PROJECTIONS Equal Area - Sinusoidal
From Robinson, Sixth Edition, page 68
9
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

10
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

11
COMMON MAP PROJECTIONS Equal Area Goodes
Homolosine
From Robinson, Sixth Edition, page 81
12
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

13
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

14
COMMON MAP PROJECTIONS Azimuthal Equidistant
From Robinson, Sixth Edition, page 85
15
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

16
COMMON MAP PROJECTIONS Azimuthal
  • Gnomic
  • All great circle arcs are straight lines
    everywhere on
  • the projection
  • Useful primarily for marine navigation

17
COMMON MAP PROJECTIONS Azimuthal
Stereographic Lamberts Equal Area Azimuthal Equ
idistant Orthographic Gnomic
From Robinson, Sixth Edition, page 84
18
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

19
COMMON MAP PROJECTIONS Special Purpose
Equidistant Cylindrical/Plane Chart
From Robinson, Sixth Edition, page 86
20
COMMON MAP PROJECTIONS Special Purpose Simple
Conic
From Robinson, Sixth Edition, page 87
21
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

22
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
23
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

24
COMMON MAP PROJECTIONS Special Purpose
Space Oblique Mercator
Robinsons
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