Procedure Syntax

Requirements: Exactly one ID statement is required.

PROC GPROJECT < option(s) >;

• ID id-variable(s) ;

PROC GPROJECT Statement

Identifies the input and output map data sets. Optionally specifies the type of projection, and 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

  • PARALEL1= latitude

  • PARALEL2= latitude

  • POLELAT= latitude

  • POLELONG= longitude

  • PROJECT=ALBERS GNOMON LAMBERT NONE

• coordinate options:

  • ASIS DUPOK

  • DEGREE

  • EASTLONG

• clipping options:

  • LATMIN= min-latitude

  • LATMAX= max-latitude

  • LONGMIN= min-longitude

  • LONGMAX= max-longitude

Options

ASIS

DUPOK

• specify that observations for which the projected values for the X and Y variables are identical to those in the previous observation should be retained. By default, successive identical observations are deleted.

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 on page 1163 and SAS Data Sets on page 29.

• Featured in: Example 4 on page 1180.

DEGREE

DEG

• specifies that the units for the longitude (X variable) and latitude (Y variable) coordinates are degrees of arc. By default, coordinate units are considered to be radians.

EASTLONG

EAST

• specifies that the longitude (X variable) values in the input map data set increase to the east. By default, longitude values increase to the west.

LATMAX= max-latitude

• specify the maximum latitude that will be 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, PROC GPROJECT treats the value of max-latitude as degrees. When PROJECT=NONE, the procedure treats the value as a Cartesian coordinate.

• Featured in: Example 3 on page 1178.

LATMIN= min-latitude

• specify the minimum latitude that will be 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, PROC GPROJECT treats the value of min-latitude as degrees. When PROJECT=NONE, the procedure treats the value as a Cartesian coordinate.

• Featured in: Example 3 on page 1178.

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

• Featured in: Example 3 on page 1178.

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: Example 3 on page 1178.

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 DATA n naming convention. That is, the procedure uses the name WORK.DATA n , 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: Example 4 on page 1180.

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 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: PARALEL1= and PARALEL2= option

PARALEL1= latitude

PARALEL2= 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

  • PARALEL1 = minlat + R / P _D

    PARALEL2 = maxlat ˆ’ 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 PARALEL1= or PARALEL2=, 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 may 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 may have to explicitly specify standard parallels that both lie on the same side of the equatMor. If this causes excessive distortion of the map, you may 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.

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. POLELAT= 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. POLELONG= 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 POLELAT= or POLELONG=, 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.

• Featured in: Example 2 on page 1177.

PROJECT=ALBERS LAMBERT GNOMON NONE

• specifies the projection method to apply to the map data set. Values for PROJECT= 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 (for example, on map data sets that have already been projected).

    By default, PROJECT=ALBERS.

  Note: There are several additional projections available. These projections are experimental and are not supported by SAS Institute Technical Support. They are: ADAMS, AITOFF, APIANUS, ARAGO, BEHRMANN, BRAUN, CYLINDRI, ECKERT1, ECKERT3, ECKERT5, EQUIRECT or MARINUS, GALL, KVRSKY7, MILLER1, MILLER2, ORTHO, PARABOLI, PETERS, PUTNINS4, ROBINSON, STEREO, WINKEL2.

  You must specify the EASTLONG option to use any of these experimental projections.

  See also: About Types of Map Projections on page 1165.

  Featured in: Example 2 on page 1177.

ID Statement

Identifies the variable or variables that define the hierarchy of the current unit areas in the input map data set.

Requirements: At least one id-variable is required.

Featured in: Example 1 on page 1174.

Syntax

• ID id-variable(s) ;

Required Arguments

id-variable(s)

• specifies one or more variables in the input map data set that identify unit areas. Id-variable can be either numeric or character.

  Each group of observations with a different ID variable value is evaluated as a separate unit area.