# Icosahedral Snyder Equal Area¶

Snyder's Icosahedral Equal Area map projections on polyhedral globes for the dodecahedron and truncated icosahedron offer relatively low scale and angular distortion. The equations involved are relatively straight-forward, and for certain instructional tools and databases, the projections are useful for world maps. The interruptions remain a disadvantage, as with any low-error projection system applied to the entire globe .

 Classification Polyhedral, equal area Available forms Forward, spherical Defined area Global Alias isea Domain 2D Input type Geodetic coordinates Output type Projected coordinates

## Parameters¶

Note

All parameters are optional for the projection.

+orient=<string>

Can be set to either `isea` or `pole`. See Snyder's Figure 12 for pole orientation .

Defaults to isea

+azi=<value>

Azimuth.

Defaults to 0.0

+aperture=<value>

Defaults to 3.0

+resolution=<value>

Defaults to 4.0

+mode=<string>

Can be either `plane`, `di`, `dd` or `hex`.

Defaults to plane

+lon_0=<value>

Central meridian/longitude of natural origin, longitude of origin or longitude of false origin (naming and meaning depend on the projection method).

Defaults to 0.0.

Note

The default convention is to interpret this value as decimal degrees. To specify radians instead, follow the value with the "r" character.

Example: +lon_0=1.570796r

+lat_0=<value>

Latitude of natural origin, latitude of false origin or latitude of projection centre (naming and meaning depend on the projection method).

Defaults to 0.0.

Note

The default convention is to interpret this value as decimal degrees. To specify radians instead, follow the value with the "r" character.

Example: +lat_0=1.570796r

+R=<value>

Radius of the sphere, given in meters. If used in conjunction with `+ellps`, `+R` takes precedence.