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)

COMMON MAP PROJECTIONSEqual 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) Mollweide’s projection. The black lines are values of 2Ω.

From Robinson, Sixth Edition, page 72

COMMON MAP PROJECTIONSEqual Area

Albers’

• Conic projection with two standard parallels

• Any two small circles, reasonably close together are

used

• Low distortion, especially along parallels

• Resembles earth’s 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

COMMON MAP PROJECTIONSEqual Area – Albers’

From Robinson, Sixth Edition, page 81

COMMON MAP PROJECTIONSEqual Area

Lambert’s

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

COMMON MAP PROJECTIONSEqual 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

COMMON MAP PROJECTIONSEqual 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

COMMON MAP PROJECTIONSEqual Area - Sinusoidal

From Robinson, Sixth Edition, page 68

COMMON MAP PROJECTIONSEqual Area

Mollweid’s

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

COMMON MAP PROJECTIONSEqual Area

Goode’s Homolosine

Combines equatorial section of sinusoidal and poleward

sections of Mollweid’s

Must be constructed from the same area scale (ie.

reference globe)

Sinusoidal and Mollweid’s have one parallel of identical

length along which they may be joined

Usually used in interrupted form

Popular in the United States

COMMON MAP PROJECTIONSEqual Area – Goode’s Homolosine

From Robinson, Sixth Edition, page 81

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

COMMON MAP PROJECTIONSAzimuthal

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

COMMON MAP PROJECTIONSAzimuthal Equidistant

From Robinson, Sixth Edition, page 85

COMMON MAP PROJECTIONSAzimuthal

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

COMMON MAP PROJECTIONSAzimuthal

Gnomic

All great circle arcs are straight lines everywhere on

the projection

Useful primarily for marine navigation

COMMON MAP PROJECTIONSAzimuthal

Stereographic

Lambert’s Equal

Area

Azimuthal

Equidistant

Orthographic

Gnomic

From Robinson, Sixth Edition, page 84

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

COMMON MAP PROJECTIONSSpecial Purpose

Equidistant Cylindrical/Plane Chart

From Robinson, Sixth Edition, page 86

COMMON MAP PROJECTIONSSpecial Purpose – Simple Conic

From Robinson, Sixth Edition, page 87

COMMON MAP PROJECTIONS

Special Purpose Map Projections, cont.

• Polyconic – not conformal or equal area

Used by the U.S. for topo sheets until 1950’s – can fit

topos together in one direction or another, but not all

• Robinson’s – 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

COMMON MAP PROJECTIONSSpecial Purpose - Polyconic

From Robinson, Sixth Edition, page 88, 89

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.

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

COMMON MAP PROJECTIONSSpecial Purpose

Robinson’s

Space

Oblique

Mercator