The GPROJECT Procedure

PROC GPROJECT Statement

Identifies the input and output map data sets. Can specify the type of projection, and the criteria for clipping and projection.

Requirements:

An input map data set is required.

Syntax

PROC GPROJECT <option(s)>;

option(s) can be one or more options from any or all of the following categories:

data set options:

DATA=input-map-data-set

OUT=output-map-data-set
projection options:

PARADIV=n

PARALLEL1=latitude

PARALLEL2=latitude

POLELAT=latitude

POLELONG=longitude

PROJECT=ALBERS | GNOMON | LAMBERT | NONE
coordinate options:

DEGREES

DUPOK

EASTLONG

NODATELINE
clipping options:

LATMIN=min-latitude

LATMAX=max-latitude

LONGMIN=min-longitude

LONGMAX=max-longitude

Options

DATA=input-map-data-set

identifies the map data set to be processed. By default, the procedure uses the most recently created SAS data set.

See also:	About the Input Map Data Set and SAS Data Sets
Featured in:	Projecting an Annotate Data Set

DEGREES

specifies that the units for the longitude (X variable) and latitude (Y variable) coordinates are degrees. By default, coordinate units are considered to be radians. The GPROJECT procedure stops processing the data set if coordinates are out of range.

Alias:

DEG

DUPOK

specify that observations be retained when their projected X and Y values are identical to those in the previous observation. By default, successive identical observations are deleted.

Note: This option is useful when you want to add annotation to a map that contains duplicate coordinates. [cautionend]

Alias:

ASIS

EASTLONG

specifies that the longitude (X variable) values in the input map data set increase to the east (that is, positive longitude values are east of the prime meridian.) By default, longitude values increase to the west.

Alias:

EAST

LATMAX=max-latitude

specify the maximum latitude that is included in the projection. Any unit areas that cross the selected latitude are clipped and closed along the specified parallels. The LATMAX= and LATMIN= options do not have to be paired; you can specify a maximum latitude without specifying a minimum.

When PROJECT=ALBERS, LAMBERT, or GNOMON, the GPROJECT procedure treats the value of max-latitude as degrees. When PROJECT=NONE, the procedure treats the value as a Cartesian coordinate.

Featured in:

Clipping an Area from the Map

LATMIN=min-latitude

specify the minimum latitude that is included in the projection. Any unit areas that cross the selected latitude are clipped and closed along the specified parallels. The LATMAX= and LATMIN= options do not have to be paired; you can specify a minimum latitude without specifying a maximum.

When PROJECT=ALBERS, LAMBERT, or GNOMON, the GPROJECT procedure treats the value of min-latitude as degrees. When PROJECT=NONE, the procedure treats the value as a Cartesian coordinate.

Featured in:

Clipping an Area from the Map

LONGMAX=max-longitude

specify the maximum longitude to be included in the projection. Any unit areas that cross the selected longitude are clipped and closed along the specified meridians. The LATMAX= and LATMIN= options do not have to be paired; you can specify a maximum longitude without specifying a minimum.

When PROJECT=ALBERS, LAMBERT, or GNOMON, the GPROJECT procedure treats the value of max-longitude as degrees. When PROJECT=NONE, the procedure treats the value as a Cartesian coordinate.

Featured in:

Clipping an Area from the Map

LONGMIN=min-longitude

specify the minimum longitude to be included in the projection. Any unit areas that cross the selected longitude are clipped and closed along the specified meridians. The LATMAX= and LATMIN= options do not have to be paired; you can specify a minimum longitude without specifying a maximum.

When PROJECT=ALBERS, LAMBERT, or GNOMON, the GPROJECT procedure treats the value of min-longitude as degrees. When PROJECT=NONE, the procedure treats the value as a Cartesian coordinate.

Featured in:

Clipping an Area from the Map

NODATELINE

enables contiguous projections for maps that cross the line between 180 degrees and -180 degrees longitude. For example, if you project a map of Asia, then the eastern tip of the continent might be projected on the left side of the map by default. The NODATELINE option enables the entire continent to be projected as a contiguous area.

OUT=output-map-data-set

names the new map data set, which contains the coordinates of the new unit areas that are created by the GPROJECT procedure.

By default, the GPROJECT procedure names the new data set that uses the DATAn naming convention. That is, the procedure uses the name WORK.DATAn, where n is the next unused number in sequence. Thus, the first automatically named data set is DATA1, the second is DATA2, and so on.

Featured in:

Projecting an Annotate Data Set

PARADIV=n

specifies the divisor that computes the values used for standard parallels for the Albers' or Lambert's projections when explicit values are not provided. By default PARADIV=4, which causes the standard parallels to be set at 1/4 and 3/4 of the range of latitude values in the input map data set.

See also:

PARALLEL1= and PARALLEL2= option

PARALLEL1=latitude PARALLEL2=latitude

specify values for the standard parallels that are used in the Albers' or Lambert's projection. Latitude must be in degrees. Positive values indicate north of the equator, and negative values indicate south of the equator. These options are ignored for the gnomonic projection.

By default, the GPROJECT procedure calculates values for the standard parallels. The defaults are chosen to minimize the distortion inherent in the projection process. The algorithm used is as follows:

PARALLEL1 = minlat + R / P_D

PARALLEL2 = maxlat - R / P_D

where:

R: is the range of latitude values in the input map data set.
P_D: is the PARADIV= value (see the discussion of the PARADIV= option).
minlat: is the minimum latitude value in the input map data set.
maxlat: is the maximum latitude value in the input map data set.

If you do not use PARALLEL1= or PARALLEL2=, or you omit either option, the GPROJECT procedure uses the calculated value for the missing parameter.

The standard parallels, whether explicitly specified or supplied by the procedure, must lie on the same side of the equator. If they do not, PROC GPROJECT prints an error message and stops (the procedure might calculate standard parallels that lie on opposite sides of the equator). When projecting a map data set that contains unit areas that cross the equator, you might have to explicitly specify standard parallels that both lie on the same side of the equator. If this causes excessive distortion of the map, you might be able to use the gnomonic projection instead of the Albers' or Lambert's projection because the gnomonic technique has no such limitations at the equator.

Alias:

PARALEL1, PARALEL2

POLELAT=latitude POLELONG=longitude

specify a projection pole to use for the gnomonic projection. The projection pole is the point at which the surface of the sphere touches the surface of the imaginary plane onto which the map is projected. The POLELAT= option specifies the latitude of the projection point.

Units for latitude are degrees; positive values indicate north of the equator, and negative values indicate south of the equator. The POLELONG= option gives the longitude for the projection point. Units for longitude are degrees; positive values indicate west of the prime meridian, and negative values indicate east of the prime meridian (unless EASTLONG also has been used in the PROC GPROJECT statement).

If you do not use the POLELAT= or POLELONG= option, or you omit either option, PROC GPROJECT uses values for the position of the center of the unit areas that are defined by the DATA= data set for the missing parameter.

Note: The map that is defined by the input map data set should not contain points more than 85 degrees (1.48353 radians) from the projection pole; all points that exceed this value are deleted from the output map data set. [cautionend]

Featured in:

Emphasizing Map Areas

PROJECT=ALBERS | LAMBERT | GNOMON | NONE

specifies the projection method to apply to the map data set. Values for the PROJECT= option are as follows:

ALBERS: specifies Albers' equal-area projection with two standard parallels.
LAMBERT: specifies Lambert's conformal projection with two standard parallels.
GNOMON: specifies the gnomonic projection, which is an azimuthal projection.
NONE: specifies that no projection should be performed. Use this option in conjunction with the LATMIN=, LATMAX=, LONGMIN=, and LONGMAX= options to perform clipping without projection.

By default, PROJECT=ALBERS.

Note: There are several additional projections available. They are: ADAMS, AITOFF, APIANUS, ARAGO, BEHRMANN, BRAUN, CYLINDRI, ECKERT1, ECKERT3, ECKERT5, EQUIRECT or MARINUS, GALL, HAMMER, KVRSKY7, MILLER1, MILLER2 , ORTHO, PARABOLI, PETERS, PUTNINS4, ROBINSON, STEREO, WINKEL2. [cautionend]

See also:	About Types of Map Projections
Featured in:	Emphasizing Map Areas

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	PARADIV=n
	PARALLEL1=latitude
	PARALLEL2=latitude
	POLELAT=latitude
	POLELONG=longitude
	PROJECT=ALBERS \| GNOMON \| LAMBERT \| NONE

	LATMIN=min-latitude
	LATMAX=max-latitude
	LONGMIN=min-longitude
	LONGMAX=max-longitude

	DATA=input-map-data-set
	OUT=output-map-data-set

	DEGREES
	DUPOK
	EASTLONG
	NODATELINE