The GREDUCE Procedure

# PROC GREDUCE Statement

Identifies the input and output map data sets. Optionally specifies the reduction criteria.

 Requirements: An input map data set is required.

### Syntax

 PROC GREDUCE ;

• data set options:  DATA=input-map-data-set OUT=output-map-data-set

• level options:  E1=min-distance E2=min-distance E3=min-distance E4=min-distance E5=min-distance N1=max-points N2=max-points N3=max-points N4=max-points N5=max-points

DATA=input-map-data-set
identifies the map data set that you want to process. By default, the procedure uses the most recently created SAS data set.

E1=min-distance
E2=min-distance
E3=min-distance
E4=min-distance
E5=min-distance
specify the minimum distance that a point must lie from a straight line segment to be included at density level 1, 2, 3, 4, or 5, respectively. That is, in a reduced curve of three points, the middle point is at least a distance that is min-distance from a straight line between the two outside points.

Express min-distance values in the units for the coordinate system of the input map data set. For example, if the input map data set contains coordinates that are expressed in radians, express the min-distance values in radians.

Specify the En= values in decreasing order. For example, the E2= value should be less than the E1= value and so on.

N1=max-points
N2=max-points
N3=max-points
N4=max-points
N5=max-points
specify that for density level 1, 2, 3, 4, or 5, the boundary of a unit area should contain no more than max-points points.

Specify the Nn= values in increasing order. For example, the N2= value should be greater than or equal to the N1= value and so on.

By default, if you omit Nn= and En = , the GREDUCE procedure calculates values for the five Nn = parameters using this formula:

Here Nmax is the maximum number of points in any unit area in the input map data set. However, the restriction that the number of points for any level cannot be less than the number of points in level 0 still applies.

OUT=output-data-set
names the new map data set, which contains all of the observations and variables in the original map data set plus the new DENSITY variable. If the input map data set contains a variable named DENSITY, the GREDUCE procedure replaces the values of the variable in the output map data set. The original values of the DENSITY variable from the input map data set are not included in the output map data set.

By default, the GREDUCE 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.