Routines (alphabetical) > Routines: M > MAP_PROJ_INIT

# MAP_PROJ_INIT

The MAP_PROJ_INIT function initializes a mapping projection (establishes the coordinate conversion mechanism for mapping points on a globe's surface to points on a plane), using either IDL's own map projections or map projections from the U.S. Geological Survey's General Cartographic Transformation Package (GCTP). GCTP version 2.0 is included with IDL.

Note: The !MAP system variable is unaffected by MAP_PROJ_INIT. To use the map projection returned by MAP_PROJ_INIT for direct or object graphics, use the MAP_PROJ_FORWARD and MAP_PROJ_INVERSE functions to convert longitude/latitude values into Cartesian (x, y) coordinates before visualization.

This routine is written in the IDL language. Its source code can be found in `map_proj_init.pro` in the `lib` subdirectory of the IDL distribution.

## Example

See MAP_PROJ_FORWARD for an example of using this function.

## Syntax

Result = MAP_PROJ_INIT( Projection [, ELLIPSOID=value] [, /GCTP] [, LIMIT=vector] [, /RADIANS] [, /RELAXED] )

Keywords/Projection Parameters: [, CENTER_AZIMUTH=value] [, CENTER_LATITUDE=value] [, CENTER_LONGITUDE=value] [, FALSE_EASTING=value] [, FALSE_NORTHING=value] [, HEIGHT=value] [, HOM_AZIM_LONGITUDE=value] [, HOM_AZIM_ANGLE=value] [, HOM_LATITUDE1=value] [, HOM_LATITUDE2=value] [, HOM_LONGITUDE1=value] [, HOM_LONGITUDE2=value] [, IS_ZONES=value] [, IS_JUSTIFY=value] [, MERCATOR_SCALE=value] [, OEA_ANGLE=value] [, OEA_SHAPEM=value] [, OEA_SHAPEN=value] [, ROTATION=value] [, SEMIMAJOR_AXIS=value] [, SEMIMINOR_AXIS=value] [, SOM_INCLINATION=value] [, SOM_LONGITUDE=value] [, SOM_PERIOD=value] [, SOM_RATIO=value] [, SOM_FLAG=value] [, SOM_LANDSAT_NUMBER=value] [, SOM_LANDSAT_PATH=value] [, SPHERE_RADIUS=value] [, STANDARD_PARALLEL=value] [, STANDARD_PAR1=value] [, STANDARD_PAR2=value] [, SAT_TILT=value] [, TRUE_SCALE_LATITUDE=value] [, ZONE=value]

## Return Value

The result is a !MAP structure containing the map parameters, which can be used as input to the map transformation functions MAP_PROJ_FORWARD and MAP_PROJ_INVERSE.

## Arguments

### Projection

Set this argument to either a projection index or a scalar string containing the name of the map projection, as described in following tables.

IDL projections:

# | Projection Name | Available Ellipsoids | Allowed Keyword Parameters
1 | Stereographic | Sphere | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
2 | Orthographic | Sphere | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
3 | Lambert Conic | Sphere | SPHERE_RADIUS, STANDARD_PAR1, STANDARD_PAR2, CENTER_LONGITUDE, CENTER_LATITUDE
4 | Lambert Azimuthal | Sphere | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
5 | Gnomonic | Sphere | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
6 | Azimuthal Equidistant | Sphere | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
7 | Satellite | Sphere | SPHERE_RADIUS, HEIGHT, SAT_TILT, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
8 | Cylindrical | Sphere | SPHERE_RADIUS, CENTER_AZIMUTH, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
9 | Mercator | Sphere | SPHERE_RADIUS, CENTER_AZIMUTH, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
10 | Mollweide | Sphere | SPHERE_RADIUS, CENTER_AZIMUTH, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
11 | Sinusoidal | Sphere | SPHERE_RADIUS, CENTER_AZIMUTH, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
12 | Aitoff | Sphere | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
13 | Hammer Aitoff | Sphere | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
14 | Albers Equal Area Conic | Sphere | SPHERE_RADIUS, STANDARD_PAR1, STANDARD_PAR2, CENTER_LONGITUDE, CENTER_LATITUDE
15 | Transverse Mercator | All | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, MERCATOR_SCALE, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
16 | Miller Cylindrical | Sphere | SPHERE_RADIUS, CENTER_AZIMUTH, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
17 | Robinson | Sphere | SPHERE_RADIUS, CENTER_AZIMUTH, CENTER_LONGITUDE, CENTER_LATITUDE, ROTATION
18 | Lambert Ellipsoid Conic | All | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, STANDARD_PAR1, STANDARD_PAR2, CENTER_LONGITUDE, CENTER_LATITUDE
19 | Goodes Homolosine | Sphere | SPHERE_RADIUS, CENTER_LONGITUDE

GCTP projections:

# | Name | Allowed Map Parameters | Notes
100 | Geographic | CENTER_LONGITUDE | No projection.
101 | UTM | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, CENTER_LONGITUDE, CENTER_LATITUDE, ZONE | All ellipsoids; cylindrical; conformal; scale is true along the center longitude.
102 | State Plane | ZONE | "Clarke 1866" or "GRS 1980" ellipsoid; uses either Transverse Mercator, Lambert Conformal Conic, or Hotine Oblique Mercator.
103 | Albers Equal Area | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, STANDARD_PAR1, STANDARD_PAR2, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; conic; equal-area; scale is true along the two standard parallels.
104 | Lambert Conformal Conic | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, STANDARD_PAR1, STANDARD_PAR2, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; conformal; scale is true along the two standard parallels.
105 | Mercator | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, CENTER_LONGITUDE, TRUE_SCALE_LATITUDE, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; cylindrical; conformal; scale is true along the true scale latitudes.
106 | Polar Stereographic | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, CENTER_LONGITUDE, TRUE_SCALE_LATITUDE, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; azimuthal; conformal; scale is true along the true scale latitude.
107 | Polyconic | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; neither conformal nor equal-area; scale is true along all parallels and along the central meridian.
108 | Equidistant Conic | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, STANDARD_PARALLEL, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; equidistant; scale is true along all meridians and along one standard parallel.
208 | Equidistant Conic | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, STANDARD_PAR1, STANDARD_PAR2, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; equidistant; scale is true along all meridians and along two standard parallels.
109 | Transverse Mercator | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, MERCATOR_SCALE, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; cylindrical; conformal; scale is true (or reduced) along the center longitude.
110 | Stereographic | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; azimuthal; conformal; scale is true at the center; directions from the center are true.
111 | Lambert Azimuthal | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; azimuthal; equal-area; scale is true at the center; directions from the center are true for spherical and polar ellipsoidal.
112 | Azimuthal Equidistant | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; azimuthal; equidistant; distances measured from the center are true; directions from the center are true; scale is true at the center.
113 | Gnomonic | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; also known as the Gnomic or Central projection; azimuthal and perspective; neither conformal nor equal-area; all great circles are straight lines; scale is true at the center; directions from the center are true.
114 | Orthographic | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; azimuthal; neither conformal nor equal-area; scale is true in the direction of latitude lines for the polar aspect; directions from the center are true.
115 | Near Side Perspective | SPHERE_RADIUS, HEIGHT, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; also known as the Vertical Perspective; azimuthal; neither conformal nor equal-area; scale is true at the center; directions from the center are true.
116 | Sinusoidal | SPHERE_RADIUS, CENTER_LONGITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; pseudocylindrical; equal-area; scale is true along the central meridian and along all parallels.
117 | Equirectangular | SPHERE_RADIUS, CENTER_LONGITUDE, TRUE_SCALE_LATITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; also known as equidistant cylindrical; neither conformal nor equal-area; scale is true along all meridians and along the true scale latitudes.
118 | Miller Cylindrical | SPHERE_RADIUS, CENTER_LONGITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; neither conformal nor equal-area; scale is true along the equator.
119 | Van der Grinten | SPHERE_RADIUS, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; neither conformal nor equal-area; scale is true along the equator.
120 | Hotine Oblique Mercator | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, MERCATOR_SCALE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING, HOM_LONGITUDE1, HOM_LATITUDE1, HOM_LONGITUDE2, HOM_LATITUDE2 | All ellipsoids; cylindrical; conformal; scale is true (or reduced) along the center line. Specified using two lat-lon points.
220 | Hotine Oblique Mercator | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, MERCATOR_SCALE, HOM_AZIM_ANGLE, HOM_AZIM_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; cylindrical; conformal; scale is true (or reduced) along the center line. Specified using azimuthal angle and longitude of the center.
121 | Robinson | SPHERE_RADIUS, CENTER_LONGITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; pseudocylindrical; neither conformal nor equal-area; scale is true along the 38° parallels.
122 | Space Oblique Mercator | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, SOM_INCLINATION, SOM_LONGITUDE, FALSE_EASTING, FALSE_NORTHING, SOM_PERIOD, SOM_RATIO, SOM_FLAG | All ellipsoids; modified cylindrical; basically conformal; scale is true along the groundtrack. Specified using inclination, longitude, period, ratio, and flag.
222 | Space Oblique Mercator | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, SOM_LANDSAT_NUMBER, SOM_LANDSAT_PATH, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; modified cylindrical; basically conformal; scale is true along the groundtrack. Specified using landsat number and path.
123 | Alaska Conformal | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; conformal; modified stereographic using complex algebra transformations to reduce scale variations.
124 | Interrupted Goode | SPHERE_RADIUS | Sphere only; pseudocylindrical; equal-area; scale is true along the central meridians and along all parallels.
125 | Mollweide | SPHERE_RADIUS, CENTER_LONGITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; pseudocylindrical; equal-area; scale is true along latitudes 40°44' N and S.
126 | Interrupted Mollweide | SPHERE_RADIUS | Sphere only; pseudocylindrical; equal-area; scale is true along the 40°44' parallels.
127 | Hammer | SPHERE_RADIUS, CENTER_LONGITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; also known as Hammer-Aitoff; based on Lambert Azimuthal; equal-area but not azimuthal; scale is true at the center.
128 | Wagner IV | SPHERE_RADIUS, CENTER_LONGITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; pseudocylindrical; equal-area; scale is true along the 42°59' parallels.
129 | Wagner VII | SPHERE_RADIUS, CENTER_LONGITUDE, FALSE_EASTING, FALSE_NORTHING | Sphere only; modification of the Hammer; equal-area; scale is true at the center.
130 | Oblated Equal Area | SPHERE_RADIUS, OEA_SHAPEM, OEA_SHAPEN, CENTER_LONGITUDE, CENTER_LATITUDE, FALSE_EASTING, FALSE_NORTHING, OEA_ANGLE | Sphere only; equal-area; lines of constant distortion follow approximately oval or rectangular paths.
131 | Integerized Sinusoidal | SPHERE_RADIUS, CENTER_LONGITUDE, FALSE_EASTING, FALSE_NORTHING, IS_ZONES, IS_JUSTIFY | Sphere only; equal-area; same as sinusoidal but with discrete latitude bands.
132 | Cylindrical Equal Area | SEMIMAJOR_AXIS, SEMIMINOR_AXIS, CENTER_LONGITUDE, STANDARD_PARALLEL, FALSE_EASTING, FALSE_NORTHING | All ellipsoids; cylindrical; equal-area; scale is true along the standard parallels (special cases: Lambert 0°, Behrmann 30°, Trystan Edwards 37.383°, Peters 44.138°, Gall orthographic 45°, Balthasart 50°.

## Keywords

Note: The following keywords apply to all projections.

### ELLIPSOID

Set this keyword to either an integer code or a scalar string containing the ellipsoid name. The default value depends upon the projection selected, but is either the Clarke 1866 (ellipsoid 0), or a sphere of radius 6370.997 km (ellipsoid 19).

The following ellipsoids are available for use with the ELLIPSOID keyword:

Index | Name | Semimajor axis (m) | Semiminor axis (m)
0 | Clarke 1866 | 6378206.4 | 6356583.8
1 | Clarke 1880 | 6378249.145 | 6356514.86955
2 | Bessel | 6377397.155 | 6356078.96284
3 | International 1967 | 6378157.5 | 6356772.2
4 | International 1909 | 6378388.0 | 6356911.94613
5 | WGS 72 | 6378135.0 | 6356750.519915
6 | Everest | 6377276.3452 | 6356075.4133
7 | WGS 66 | 6378145.0 | 6356759.769356
8 | GRS 1980 | 6378137.0 | 6356752.31414
9 | Airy | 6377563.396 | 6356256.91
10 | Modified Everest | 6377304.063 | 6356103.039
11 | Modified Airy | 6377340.189 | 6356034.448
12 | Walbeck | 6378137.0 | 6356752.314245
13 | Southeast Asia | 6378155.0 | 6356773.3205
14 | Australian National | 6378160.0 | 6356774.719
15 | Krassovsky | 6378245.0 | 6356863.0188
16 | Hough | 6378270.0 | 6356794.343479
17 | Mercury 1960 | 6378166.0 | 6356784.283666
18 | Modified Mercury 1968 | 6378150.0 | 6356768.337303
19 | Sphere | 6370997.0 | 6370997.0
20 | Clarke IGN | 6378249.2 | 6356515.0
21 | Helmert 1906 | 6378200.0 | 6356818.2
22 | Modified Fischer 1960 | 6378155.0 | 6356773.3
23 | South American 1969 | 6378160.0 | 6356774.7
24 | WGS 84 | 6378137.0 | 6356752.314245

Note: For many projections, you can specify your own ellipsoid by using either the SEMIMAJOR_AXIS and SEMIMINOR_AXIS or the SPHERE_RADIUS keywords.

### GCTP

Set this keyword to indicate that the GCTP library should be used for the projection. By default, MAP_PROJ_INIT uses the IDL projection library. This keyword is ignored if the projection exists only in one system (GCTP or IDL), or if the Projection argument is specified as an index.

### LIMIT

Set this keyword to a four-element vector of the form

[Latmin, Lonmin, Latmax, Lonmax]

that specifies the boundaries of the region to be mapped. (Lonmin, Latmin) and (Lonmax, Latmax) are the longitudes and latitudes of two points diagonal from each other on the region's boundary.

Note: If the longitude range in LIMIT is less than or equal to 180 degrees, map clipping is performed in lat/lon coordinates before the transform. If the longitude range is greater than 180 degrees, map clipping is done in Cartesian coordinates after the transform. For non-cylindrical projections, clipping after the transformation to Cartesian coordinates means that some lat/lon points that fall outside the bounds specified by LIMIT may not be clipped. This occurs when the transformed lat/lon points fall inside the cartesian clipping rectangle.

Note: Lonmin should be in the range –180 to +180. Lonmax should be in the range –180 to +540, and must be greater than Lonmin. The total range for the map (Lonmax – Lonmin) must be 360 degrees or less.

### RADIANS

Set this keyword to indicate that all parameters that represent angles are specified in radians rather than degrees.

### RELAXED

If this keyword is set, any projection parameters which do not apply to the specified projection will be quietly ignored. By default, MAP_PROJ_INIT will issue errors for parameters that do not apply to the specified projection.

## Projection Keywords

The following keywords apply only to some projections. Consult the tables above to determine which keywords apply to the projection you have selected.

Note: Unless the RADIANS keyword is set, all angles are measured in degrees, specified as a floating-point value.

### CENTER_AZIMUTH

Set this keyword to the angle of the central azimuth, in degrees east of North. The default is 0 degrees. The pole is placed at an azimuth of CENTRAL_AZIMUTH degrees counterclockwise of North, as specified by the ROTATION keyword.

### CENTER_LATITUDE

Set this keyword to the latitude of the point on the earth's surface to be mapped to the center of the projection plane. Latitude is measured in degrees North of the equator and must be in the range: -90 to +90. The default value is zero.

Note: For the GCTP UTM projection, the actual value of the center latitude is ignored, and only the sign (positive or negative) is used. If CENTER_LATITUDE is zero or greater then the UTM zone is positive (Northern hemisphere). If CENTER_LATITUDE is less than zero then the UTM zone is negative (Southern hemisphere). If ZONE is supplied then CENTER_LATITUDE is ignored.

Note: For the Hotine Oblique Mercator projection, the center latitude should not be set to 0, +90, or -90.

Note: For the GCTP Polar Stereographic projection, if the TRUE_SCALE_LATITUDE is greater than or equal to zero, the center latitude will automatically be set to +90 (the North pole). If the TRUE_SCALE_LATITUDE is less than zero, the center latitude will automatically be set to -90 (the South pole).

### CENTER_LONGITUDE

Set this keyword to the longitude of the point on the earth's surface to be mapped to the center of the map projection. Longitude is measured in degrees east of the Greenwich meridian and must be in the range: -180 to +360. The default value is zero.

Note: For stereographic projections centered on the North or South pole, CENTER_LONGITUDE specifies the longitude directly below the pole.

Note: For the GCTP UTM projection, the center longitude is used to determine the UTM zone, along with the CENTER_LATITUDE to determine whether the zone is in the Northern or Southern hemisphere. If ZONE is supplied then CENTER_LONGITUDE is ignored.

### FALSE_EASTING

Set this keyword to the false easting value (in meters) to be added to each x coordinate for the forward transform, or subtracted from each x coordinate for the inverse transform.

### FALSE_NORTHING

Set this keyword to the false northing value (in meters) to be added to each y coordinate for the forward transform, or subtracted from each y coordinate for the inverse transform.

### HEIGHT

Set this keyword to the height (in meters) above the earth's surface for satellite projections. The default value is 35800 km.

### HOM_AZIM_LONGITUDE

Set this keyword to the longitude in degrees of the central meridian point where the azimuth occurs.

### HOM_AZIM_ANGLE

Set this keyword to the azimuth angle, measured in degrees, east of a north-south line that intersects the center line. The center line is defined as the great circle path along which the Mercator cylinder touches the sphere.

### HOM_LATITUDE1

Set this keyword to the latitude in degrees of the first point on the center line. The center line is defined as the great circle path along which the Mercator cylinder touches the sphere.

Note: HOM_LATITUDE1 cannot be equal to HOM_LATITUDE2.

### HOM_LATITUDE2

Set this keyword to the latitude in degrees of the second point on the center line. The center line is defined as the great circle path along which the Mercator cylinder touches the sphere.

Note: HOM_LATITUDE1 cannot be equal to HOM_LATITUDE2.

### HOM_LONGITUDE1

Set this keyword to the longitude in degrees of the first point on the center line. The center line is defined as the great circle path along which the Mercator cylinder touches the sphere.

### HOM_LONGITUDE2

Set this keyword to the longitude in degrees of the second point on the center line. The center line is defined as the great circle path along which the Mercator cylinder touches the sphere.

### IS_ZONES

Set this keyword to the number of longitudinal zones to include in the projection.

### IS_JUSTIFY

Set this keyword to a flag indicating what to do with rows with an odd number of columns. The possible values are:

0 | Indicates the extra column is on the right of the projection Y axis
1 | Indicates the extra column is on the left of the projection Y axis
2 | Calculate an even number of columns

### MERCATOR_SCALE

Set this keyword to the scale factor at the central meridian (Transverse Mercator projection) or the center of the projection (Hotine Oblique Mercator projection). For the Transverse Mercator projection, the default scale is 0.9996.

### OEA_ANGLE

Set this keyword to the Oblated Equal Area oval rotation angle in degrees.

### OEA_SHAPEM

Set this keyword to the Oblated Equal Area shape parameter m. The value of OEA_SHAPEM determines the horizontal flatness of the oblong region, and is usually set to a value between one and three.

### OEA_SHAPEN

Set this keyword to the Oblated Equal Area oval shape parameter n. The value of OEA_SHAPEN determines the vertical flatness of the oblong region, and is usually set to a value between one and three.

Note: Setting both OEA_SHAPEM and OEA_SHAPEN equal to two is equivalent to using the Lambert Azimuthal projection.

### ROTATION

Set this keyword to the angle through which the North direction should be rotated around the line between the earth's center and the point (CENTER_LONGITUDE, CENTER_LATITUDE). ROTATION is measured in degrees with the positive direction being clockwise rotation around the line. Values should be in the range ‑180 to +180. The default value is zero.

Note: If the center of the map is at the North pole, North is in the direction CENTER_LONGITUDE + 180. If the origin is at the South pole, North is in the direction CENTER_LONGITUDE.

### SEMIMAJOR_AXIS

Set this keyword to the length (in meters) of the semimajor axis of the reference ellipsoid. The default is either the Clarke 1866 ellipsoid (6378206.4 m) or the Sphere radius (6370997 m), depending upon the projection.

### SEMIMINOR_AXIS

Set this keyword to the length (in meters) of the semiminor axis of the reference ellipsoid. The default is either the Clarke 1866 ellipsoid (6356583.8 m) or the Sphere radius (6370997 m), depending upon the projection.

### SOM_INCLINATION

Set this keyword to the orbit inclination angle in degrees of the ascending node, counter-clockwise from equator.

### SOM_LONGITUDE

Set this keyword to the longitude in degrees of the ascending orbit at the equator.

### SOM_PERIOD

Set this keyword to the period in minutes of the satellite revolution.

### SOM_RATIO

Set this keyword to the Landsat ratio to compensate for confusion at the northern end of orbit. A typical value is 0.5201613.

### SOM_FLAG

Set this keyword to the end of path flag for Landsat, where 0 is the start and 1 is the end.

### SOM_LANDSAT_NUMBER

Set this keyword to the Landsat satellite number.

### SOM_LANDSAT_PATH

Set this keyword to the Landsat path number (use 1 for Landsat 1, 2 and 3; use 2 for Landsat 4 and 5).

### SPHERE_RADIUS

Set this keyword to the radius (in meters) of the reference sphere. The default is 6370997 m.

### STANDARD_PARALLEL

Set this keyword to the latitude in degrees of the standard parallel along which the scale is true. The value must be between -90 and 90.

### STANDARD_PAR1

Set this keyword to the latitude in degrees of the first standard parallel along which the scale is true. The value must be between -90 and 90.

Note: For Albers Equal Area and Lambert Conformal Conic projections, STANDARD_PAR1 and STANDARD_PAR2 should not be set to values that are equal and opposite.

### STANDARD_PAR2

Set this keyword to the latitude in degrees of the second standard parallel along which the scale is true. The value must be between -90 and 90.

Note: For Albers Equal Area and Lambert Conformal Conic projections, STANDARD_PAR1 and STANDARD_PAR2 should not be set to values that are equal and opposite.

### SAT_TILT

Set this keyword to the downward tilt in degrees of the camera, in degrees from the projection horizontal.

### TRUE_SCALE_LATITUDE

Set this keyword to the latitude in degrees of true scale.

### ZONE

Set this keyword to an integer giving the zone for the GCTP UTM projection or GCTP State Plane projection.

Note: For the UTM projection, you may also use the CENTER_LONGITUDE and CENTER_LATITUDE keywords to set the zone. Internally, the ZONE value will be computed from the longitude and latitude.

Note: For UTM, the zone number should be in the range -60 to -1 (Southern Hemisphere) or 1 to 60 (Northern Hemisphere).

The following table lists the allowed zones for the State Plane projection:

State | Jurisdiction Zone | NAD27 Zone Code | NAD83 Zone Code
Alabama | East | 0101 | 0101
West | 0102 | 0102
Alaska | 01 through 10 | 5001 ... 5010 | 5001 ... 5010
Arizona | East | 0201 | 0201
Central | 0202 | 0202
West | 0203 | 0203
Arkansas | North | 0301 | 0301
South | 0302 | 0302
California | 01 through 07 | 0401 ... 0407 | 0401 ... 0406
Colorado | North | 0501 | 0501
Central | 0502 | 0502
South | 0503 | 0503
Connecticut | 0600 | 0600
Delaware | 0700 | 0700
District of Columbia | 1900 | 1900
Florida | East | 0901 | 0901
West | 0902 | 0902
North | 0903 | 0903
Georgia | East | 1001 | 1001
West | 1002 | 1002
Hawaii | 01 through 05 | 5101 ... 5105 | 5101 ... 5105
Idaho | East | 1101 | 1101
Central | 1102 | 1102
West | 1103 | 1103
Illinois | East | 1201 | 1201
West | 1202 | 1202
Indiana | East | 1301 | 1301
West | 1302 | 1302
Iowa | North | 1401 | 1401
South | 1402 | 1402
Kansas | North | 1501 | 1501
South | 1502 | 1502
Kentucky | North | 1601 | 1601
South | 1602 | 1602
Louisiana | North | 1701 | 1701
South | 1702 | 1702
Offshore | 1703 | 1703
Maine | East | 1801 | 1801
West | 1802 | 1802
Maryland | 1900 | 1900
Massachusetts | Mainland | 2001 | 2001
Island | 2002 | 2002
Michigan | East (Transverse Mercator) | 2101 | -----
Central (Transverse Mercator) | 2102 | -----
West (Transverse Mercator) | 2103 | -----
North (Lambert) | 2111 | 2111
Central (Lambert) | 2112 | 2112
South (Lambert) | 2113 | 2113
Minnesota | North | 2201 | 2201
Central | 2202 | 2202
South | 2203 | 2203
Mississippi | East | 2301 | 2301
West | 2302 | 2302
Missouri | East | 2401 | 2401
Central | 2402 | 2402
West | 2403 | 2403
Montana | ----- | 2500
| North | 2501 | -----
Central | 2502 | -----
South | 2503 | -----
Nebraska | ----- | 2600
| North | 2601 | -----
South | 2602 | -----
Nevada | East | 2701 | 2701
Central | 2702 | 2702
West | 2703 | 2703
New Hampshire | 2800 | 2800
New Jersey | 2900 | 2900
New Mexico | East | 3001 | 3001
Central | 3002 | 3002
West | 3003 | 3003
New York | East | 3101 | 3101
Central | 3102 | 3102
West | 3103 | 3103
Long Island | 3104 | 3104
North Carolina | 3200 | 3200
North Dakota | North | 3301 | 3301
South | 3302 | 3302
Ohio | North | 3401 | 3401
South | 3402 | 3402
Oklahoma | North | 3501 | 3501
South | 3502 | 3502
Oregon | North | 3601 | 3601
South | 3602 | 3602
Pennsylvania | North | 3701 | 3701
South | 3702 | 3702
Rhode Island | 3800 | 3800
South Carolina | ----- | 3900
| North | 3901 | -----
South | 3902 | -----
South Dakota | North | 4001 | 4001
South | 4002 | 4002
Tennessee | 4100 | 4100
Texas | North | 4201 | 4201
North Central | 4202 | 4202
Central | 4203 | 4203
South Central | 4204 | 4204
South | 4205 | 4205
Utah | North | 4301 | 4301
Central | 4302 | 4302
South | 4303 | 4303
Vermont | 4400 | 4400
Virginia | North | 4501 | 4501
South | 4502 | 4502
Washington | North | 4601 | 4601
South | 4602 | 4602
West Virginia | North | 4701 | 4701
South | 4702 | 4702
Wisconsin | North | 4801 | 4801
Central | 4802 | 4802
South | 4803 | 4803
Wyoming | East | 4901 | 4901
East Central | 4902 | 4902
West Central | 4903 | 4903
West | 4904 | 4904
Puerto Rico | 5201 | 5200
Virgin Islands | ----- | 5200
| St. John, St. Thomas | 5201 | -----
St. Croix | 5202 | -----
American Samoa | 5300 | -----
Guam | 5400 | -----

## Version History

5.6 | Introduced
7.1 | Deprecated the DATUM keyword Added the ELLIPSOID keyword
8.0 | Added Geographic projection, Added Cylindrical Equal Area projection, Added ellipsoid support to Lambert Azimuthal

## See Also

MAP_PROJ_FORWARD, MAP_PROJ_INVERSE, MAP_PROJ_IMAGE