# Selecting a Projection

## Definitions

Conformal: Preserves shape but not size (area or distance)

Equal-Area: Preserves area but not shape or size

Equidistant: Preserves the length of lines but not shape of size

Rhumb line: lines crossing lines of latitude (parallels) and lines of longitude (meridians) at the same angle. See: http://en.wikipedia.org/wiki/Rhumb

## Selection

The list below can help select the best map projection for a given area and the characteristics you would like maintained in the projected map. Start with the area you wish to represent and then work your way through the list to find the projection method to use.

- World (Earth should be treated as a sphere)
- Conformal (gross area distortion)
- Constant scale along Equator
- Mercator

- Constant scale along meridian
- Transverse Mercator

- Constant scale along oblique great circle
- Oblique Mercator

- Entire Earth shown
- Lagrange
- August
- Eisenlohr

- Constant scale along Equator
- Equal-Area
- Standard without interruption
- Hammer
- Mollweide
- Eckert IV or VI
- McBryde or McBryde-Thomas variations
- Boggs Eumorphic
- Sinusoidal
- misc. pseudocylindricals

- Interrupted for land or ocean
- Any of above except Hammer
- Goode Homolosine

- Oblique aspect to group continents
- Briesemeister
- Oblique Mollweide

- Standard without interruption
- Equidistant
- Centered on pole
- Polar Azimuthal Equidistant

- Centered on a city
- Oblique Azimuthal Equidistant

- Centered on pole
- Straight rhumb lines
- Mercator

- Compromise distortion
- Miller Cylindrical
- Robinson

- Conformal (gross area distortion)
- Hemisphere (Earth should be treated as a sphere)
- Conformal
- Stereographic (any aspect)

- Equal-Area
- Lambert Azimuthal Equal-Area (any aspect)

- Equidistant
- Azimuthal Equidistant (any aspect)

- Global look
- Orthographic (any aspect)

- Conformal
- Continent, ocean, or smaller region (Earth should be treated as a sphere for larger continents and oceans and as an ellipsoid for smaller regions, especially at a larger scale)
- Predominant east-west extent
- Along Equator
- Conformal
- Mercator

- Equal-Area
- Cylindrical Equal-Area

- Conformal
- Away from Equator
- Conformal
- Lambert Conformal Conic

- Equal-Area
- Albers Equal-Area Conic

- Conformal

- Along Equator
- Predominant north-south extent
- Conformal
- Transverse Mercator

- Equal-Area
- Transverse Cylindrical Equal-Area

- Conformal
- Predominant oblique extent (for example: North America, South America, Atlantic Ocean)
- Conformal
- Oblique Mercator

- Equal-Area
- Oblique Cylindrical Equal-Area

- Conformal
- Equal extent in all directions (for example: Europe, Africa, Asia, Australia, Antarctica, Pacific Ocean, Indian Ocean, Arctic Ocean, Antarctic Ocean)
- Center at pole
- Conformal
- Polar Stereographic

- Equal-Area
- Polar Lambert Azimuthal Equal-Area

- Conformal
- Center along Equator
- Conformal
- Equatorial Stereographic

- Equal-Area
- Equatorial Lambert
- Azimuthal Equal-Area

- Conformal
- Center away from pole or Equator
- Conformal
- Oblique Stereographic

- Equal-Area
- Oblique Lambert
- Azimuthal Equal-Area

- Conformal

- Center at pole
- Straight rhumb lines (principally for oceans)
- Mercator

- Straight great-circle routes
- Gnomonic (for less than hemisphere)

- Correct scale along meridians
- Center at pole
- Polar Azimuthal Equidistant

- Center along Equator
- Plate Carree (Equidistant Cylindrical)

- Center away from pole or Equator
- Equidistant Conic

- Center at pole

From: Map Projections - A Working Manual By JOHN P. SNYDER, U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1395