Map Projections: (342 Geospatial Reference Data - Input Conventions)
Every flat map misrepresents the surface of the Earth in some way. A map or parts of a map can show one or more -- but never all -- of the following: true directions; true distances; true areas; true shapes.
On an equidistant map, distances are true only along particular lines such as those radiating from a single point selected as the center of the projection. Shapes are more or less distorted on every equal-area map. Sizes of areas are distorted on conformal maps even though shapes of small areas are shown correctly. The degree and kinds of distortion vary with the projection used in making a map of a particular area. Some projections are suited for mapping large areas that are mainly north-south in extent, others for large areas that are mainly east-west in extent, and still others for large areas that are oblique to the Equator.
The subfields used in field 342 for each map projection are identified as follows:
|
Projection: |
Subfields used: |
|
Albers conical equal area |
a, e, g, h, i, j |
|
Azimuthal equidistant |
a, g, h, i, j |
|
Equidistant conic |
a, e, g, h, i, j |
|
Equirectangular |
a, e, g, i, j |
|
General vertical near-sided perspective |
a, l, g, h, i, j |
|
Gnomonic |
a, g, h, i, j |
|
Lambert azimuthal equal area |
a, g, h, i, j |
|
Lambert conformal conic |
a, e, g, h, i, j |
|
Mecator |
a, e or k, g, i, j |
|
Modified stereographic for Alaska |
a, i, j, a, g, i, j |
|
Oblique Mercator |
a, k, m and n or e f e f, h, i, j |
|
Orthographic |
a, g, h, i, j |
|
Polar stereographic |
a, n, e or k, i, j |
|
Polyconic |
a, g, h, i, j |
|
Robinson |
a, g, i, j |
|
Sinusoidal |
a, g, i, j |
|
Space oblique Mercator |
a, o, i, j |
|
Stereographic |
a, g, h, i, j |
|
Transverse Mercator |
a, k, g, h, i, j |
|
Van der Grinten |
a, g, i, j |
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