Cartographic projection

The foundation of PROJ is the large number of projections available in the library. This section is devoted to the generic parameters that can be used on any projection in the PROJ library.

Below is a list of PROJ parameters which can be applied to most coordinate system definitions. This table does not attempt to describe the parameters particular to particular projection types. These can be found on the pages documenting the individual projections.




Semimajor radius of the ellipsoid axis


Axis orientation


Semiminor radius of the ellipsoid axis


Ellipsoid name (see proj -le)


Scaling factor (deprecated)


Scaling factor


Latitude of origin


Central meridian


Center longitude to use for wrapping (see below)


Allow longitude output outside -180 to 180 range, disables wrapping (see below)


Alternate prime meridian (typically a city name, see below)


Projection name (see proj -l)


meters, US survey feet, etc.


vertical units.


False easting


False northing

In the sections below most of the parameters are explained in details.


Horizontal units can be specified using the +units keyword with a symbolic name for a unit (i.e. us-ft). Alternatively the translation to meters can be specified with the +to_meter keyword (i.e. 0.304800609601219 for US feet). The -lu argument to cs2cs or proj can be used to list symbolic unit names. The default unit for projected coordinates is the meter. A few special projections deviate from this behavior, most notably the latlong pseudo-projection that returns degrees.

Vertical (Z) units can be specified using the +vunits keyword with a symbolic name for a unit (i.e. us-ft). Alternatively the translation to meters can be specified with the +vto_meter keyword (i.e. 0.304800609601219 for US feet). The -lu argument to cs2cs or proj can be used to list symbolic unit names. If no vertical units are specified, the vertical units will default to be the same as the horizontal coordinates.


proj does not handle vertical units at all and hence the +vto_meter argument will be ignored.

Scaling of output units can be done by applying the +k_0 argument. The returned coordinates are scaled by the value assigned with the +k_0 parameter.

Input units for parameters that can be understood to be either decimal degrees or radians are interpreted to be decimal degrees by convention.

Explicit specification of input units can be accomplished by adding the appropriate suffix to input values.




Decimal degrees






Example of use. The longitude of the central meridian +lon_0=90, can also be expressed more explicitly with units of decimal degrees as +lon_0=90d or in radian units as +lon_0=1.570796r (approximately).

False Easting/Northing

Virtually all coordinate systems allow for the presence of a false easting (+x_0) and northing (+y_0). Note that these values are always expressed in meters even if the coordinate system is some other units. Some coordinate systems (such as UTM) have implicit false easting and northing values.

Longitude Wrapping

By default PROJ wraps output longitudes in the range -180 to 180. The +over switch can be used to disable the default wrapping which is done at a low level in pj_inv(). This is particularly useful with projections like the Equidistant Cylindrical (Plate Carrée) or Mercator where it could be desirable for X values past -20000000 (roughly) to continue past -180 instead of wrapping to +180.

Note however that for most projections where the 180 meridian does not project to a straight line, +over will have no effect or will not lead to expected results.

The +lon_wrap option can be used to provide an alternative means of doing longitude wrapping within pj_transform(). The argument to this option is a center longitude. So +lon_wrap=180 means wrap longitudes in the range 0 to 360. Note that +over does not disable +lon_wrap.

Prime Meridian

A prime meridian may be declared indicating the offset between the prime meridian of the declared coordinate system and that of greenwich. A prime meridian is declared using the "pm" parameter, and may be assigned a symbolic name, or the longitude of the alternative prime meridian relative to greenwich.

Currently prime meridian declarations are only utilized by the pj_transform() API call, not the pj_inv() and pj_fwd() calls. Consequently the user utility cs2cs does honour prime meridians but the proj user utility ignores them.

The following predeclared prime meridian names are supported. These can be listed using with cs2cs -lm.





























Example of use. The location long=0, lat=0 in the greenwich based lat/long coordinates is translated to lat/long coordinates with Madrid as the prime meridian.

cs2cs +proj=latlong +datum=WGS84 +to +proj=latlong +datum=WGS84 +pm=madrid
0 0
3d41'16.48"E    0dN 0.000

Axis orientation

Starting in PROJ 4.8.0, the +axis argument can be used to control the axis orientation of the coordinate system. The default orientation is "easting, northing, up" but directions can be flipped, or axes flipped using combinations of the axes in the +axis switch. The values are:

  • "e" - Easting

  • "w" - Westing

  • "n" - Northing

  • "s" - Southing

  • "u" - Up

  • "d" - Down

They can be combined in +axis in forms like:

  • +axis=enu - the default easting, northing, elevation.

  • +axis=neu - northing, easting, up - useful for "lat/long" geographic coordinates, or south orientated transverse mercator.

  • +axis=wnu - westing, northing, up - some planetary coordinate systems have "west positive" coordinate systems


The +axis argument does not work with the proj command line utility.