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The GCONTOUR Procedure

PLOT Statement

Creates contour plots using values of three numeric variables from the input data set as the source of the contour coordinates.

Requirements: A plot request is required.
Global statements: AXIS, FOOTNOTE, LEGEND, PATTERN, SYMBOL, TITLE


Description

The PLOT statement specifies the three variables to plot. Optionally, it controls the contour levels, labels the plot lines, and modifies axes as well as the general appearance of the graph. Only one plot request can be specified in a PLOT statement. To specify multiple plots for a single PROC GCONTOUR statement, use multiple PLOT statements.

The PLOT statement automatically

Note:   You cannot produce overlaid contour plots with PROC GCONTOUR alone.  [cautionend]

You can use global statements to modify the axes, the legend, the contour lines and contour line labels, and the fill patterns and pattern colors for contour areas. You can also add titles, footnotes, and notes to the chart, and you can use an Annotate data set to enhance the chart.

Syntax

PLOT plot-request </option(s)>;

plot-request must be

y*x=z

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

Required Arguments

y*x=z
specifies three numeric variables from the input data set:
y is the variable that is plotted on the vertical (y) axis.
x is the variable that is plotted on the horizontal (x) axis.
z is the variable that is plotted as contour lines.

Options

You can specify as many PLOT options as you want, and you can list them in any order. If you use a BY statement on the procedure, the options in each PLOT statement affect all graphs produced by that BY statement.

ANNOTATE=Annotate-data-set
ANNO=Annotate-data-set
specifies a data set to annotate charts produced by the PLOT statement.
See also: The Annotate Data Set

AUTOHREF
draws reference lines at all major tick marks on the horizontal axis.

AUTOLABEL | AUTOLABEL=(autolabel_suboptions)
automatically labels the contour lines. Autolabel-suboptions can be one or more of the suboptions described in Autolabel Suboptions.

The label for each contour line is the z value for that contour level. By default, labels are displayed in BEST format. To change the format, use a FORMAT statement.

When AUTOLABEL is used, the LLEVELS= and CLEVELS= options are ignored and the SYMBOL statement controls label text and contour-line attributes. For more information on the SYMBOL statement, see Modifying Contour Lines and Labels with the SYMBOL Statement.

Even though AUTOLABEL labels the contour lines, a default legend is still generated. To suppress the legend, use the NOLEGEND option.
Featured in: Labeling Contour Lines

AUTOVREF
draws reference lines at all major tick marks on the vertical axis.

CAXIS=axis-color
specifies a color for axis lines and all major and minor tick marks. By default, axes are displayed in the second color in the colors list.

If you use the CAXIS= option, it may be overridden by the COLOR= suboption of the MAJOR= or MINOR= option in an AXIS definition.

CFRAME=background-color
CFR=background-color
fills the axis area with the specified color and automatically draws a frame around the axis area.

CHREF=reference-line-color
CH=reference-line-color
specifies the color for reference lines that are requested by the HREF= option. By default, these lines are displayed in the axis color.

CLEVELS=color(s)
specifies a list of colors for plot contour levels. The number of specified colors should correspond to the number of contour levels since one color represents each level of contour. If fewer colors are specified than the number of levels in the plot, the procedure provides default colors from the current colors list. The procedure default is to rotate through the current colors list for each line type.

This option is ignored if AUTOLABEL is used.

COUTLINE=outline-color
specifies a color for outlining filled areas. This option is ignored unless the PATTERN option is also used. By default, the outline color is the same as the color of the filled area.

Note:   The outline color is the only distinction between empty patterns. Use of this option makes the patterns look the same when VALUE=EMPTY in PATTERN definitions.  [cautionend]
Featured in: Using Patterns and Joins

CTEXT=text-color
specifies a color for all text on the axes and legend, including axis labels, tick mark values, legend labels, and legend value descriptions.

If you omit the CTEXT= option, a color specification is searched for in this order:

  1. specified colors on assigned AXIS and LEGEND statements

  2. the CTEXT= option in a GOPTIONS statement

  3. the default, the first color in the colors list.

For legend text, colors that you specify on an assigned LEGEND statement override CTEXT=. Thus, a LEGEND statement's VALUE= color is used for legend values, and its LABEL= color is used for legend labels.

For axes text, colors that you explicitly specify for values and labels on an assigned AXIS statement override CTEXT=. Thus, an AXIS statement's VALUE= color is used for axis values, and its LABEL= color is used for axis labels. However, if the AXIS statement specifies only general axis colors with its COLOR= option, the CTEXT= color overrides that general specification and is used for axis labels and values; the COLOR= color is still used for all other axis colors, such as tick marks.

If you use a BY statement in the procedure, the color of the BY variable labels is controlled by the CBY= option in the GOPTIONS statement.
Featured in: Using Patterns and Joins

CVREF=reference-line-color
CV=reference-line-color
specifies the color for reference lines that are requested by the VREF= option. By default, these lines are displayed in the axis color.

DESCRIPTION='entry-description'
DES='entry-description'
specifies the description of the catalog entry for the chart. The maximum length for entry-description is 40 characters. The description does not appear on the chart. By default, the GCONTOUR procedure assigns a description of the form PLOT OF y*x=z, where y*x=z is the request specified in the PLOT statement.

GRID
draws reference lines at all major tick marks on both axes. This is the same as specifying both AUTOHREF and AUTOVREF.

HAXIS=AXIS<1...99>
assigns axis characteristics from the corresponding AXIS definition to the horizontal (x) axis.
See also: AXIS Statement
Featured in: Labeling Contour Lines

HMINOR=number-of-minor-ticks
HM=number-of-minor-ticks
specifies the number of minor tick marks to use between each major tick mark on the horizontal (x) axis. No values are displayed for minor tick marks. HMINOR= overrides the MINOR= option in an AXIS definition assigned to the horizontal (x) axis.

HREF=value-list
draws one or more reference lines perpendicular to the horizontal axis at points specified by value-list. See the LEVELS= option for a description of value-list.

HREVERSE
specifies that the order of the values on the horizontal axis be reversed.

JOIN
combines adjacent grid cells with the same pattern to form a single pattern area. This option is ignored unless the PATTERN option is also used.
Featured in: Using Patterns and Joins

LEGEND=LEGEND<1...99>
assigns legend characteristics to the legend to adjust the location, text, and appearance of axes on the plots. The option value indicates which LEGEND definition to use. To suppress the legend, use the NOLEGEND option. The LEGEND= option is ignored if the specified LEGEND definition is not currently in effect.

If you use the SHAPE= option in a LEGEND statement, the value LINE is valid. If you use the PATTERN option, SHAPE=BAR is also valid.
See also: LEGEND Statement
Featured in: Labeling Contour Lines

LEVELS=value-list
specifies values of z for plot contour levels and therefore changes the number of contour levels. You can specify up to 100 values. By default, the GCONTOUR procedure plots seven contour levels for z. These levels occur at every 15th percent of the range between the 5th and 95th percentiles.

For numeric variables, value-list can be an explicit list of values, a starting and an ending value with an interval increment, or a combination of both forms:

If a numeric variable has an associated format, the specified values must be the unformatted values.

By default, the GCONTOUR procedure selects colors and line types for the contour levels by rotating through the colors list for each line type (1 through 46) until all the levels have been represented. The level lines on the plot represent the intersection of a plane, parallel to the x-y plane, and the surface that is formed by the data at the z value. See Selecting Contour Levels for more information.

You can specify the colors and line types for contour levels. The way to do this depends on whether AUTOLABEL is used:

As an alternative to representing contour levels with contour lines, you can use the PATTERN option to fill each level with a solid pattern or with the colors and patterns specified in PATTERN statements.
Featured in: Labeling Contour Lines and Specifying Contour Levels

LHREF=line-type
LH=line-type
specifies the line type for drawing reference lines that are requested by the HREF= option. Line-type is a number from 1 to 46. The default is LHREF=1, a solid line. See Specifying Line Types for available line types.

LLEVELS=line-type-list
lists numbers for line types for plot contour lines. Each line type represents one contour level, so the number of line types listed should correspond to the number of contour levels. Thus, for a contour plot that uses the default seven levels, specify seven line types.

If fewer line types are specified than the number of levels in the plot, the procedure provides default line types. With the default, contour levels rotate through line types 1 through 46, displaying each line type in all of the colors in the colors list before moving to the next line type. See Specifying Line Types for available line types.

For colors and lines specified with both the CLEVELS= and LLEVELS= options, the first contour level is displayed in the first color in the CLEVELS= color list and in the first line type specified with the LLEVELS= option. The second level is displayed in the second color and the second line type, and so on.

This option is ignored if AUTOLABEL is used.
Featured in: Specifying Contour Levels

LVREF=line-type
LV=line-type
specifies the line type for drawing reference lines that are requested by the VREF= option. Line-type is a number from 1 to 46. The default is LVREF=1, a solid line. See Specifying Line Types for available line types.

NAME='entry-name'
specifies the name of the catalog entry for the graph. The maximum length for entry-name is 8 characters. The default name is GCONTOUR. If the specified name duplicates the name of an existing entry, SAS/GRAPH software adds a number to the duplicate name to create a unique entry, for example, GCONTOU1.

NLEVELS=number-of-levels
specifies the number of contour levels to plot. Values can be integers from 1 to 100, inclusive. The contour levels are computed as follows, where L represents an array of levels:

NOAXIS
NOAXES
specifies that a plot have no axes, axis values, or axis labels. The frame is displayed around the plot unless you use the NOFRAME option.

NOFRAME
suppresses the frame that is drawn by default around the plot area.

NOLEGEND
suppresses the plot legend that describes contour levels and their line types or fill patterns and colors.

PATTERN
specifies the fill pattern and pattern colors for contour areas. The plot contour levels are represented by rectangles filled with patterns. The pattern for each rectangle is determined by calculating the mean of the values of the z variable for the four corners of the rectangle and assigning the pattern for the level closest to the mean.

By default, the procedure uses a solid pattern for the levels and rotates the pattern through the colors list. If the V6COMP option is in effect for the GOPTIONS statement, cross-hatch patterns are used instead of solid patterns. To explicitly define patterns, use PATTERN definitions for map/plot patterns.
See also: Selecting Contour Levels
Featured in: Using Patterns and Joins

VAXIS=AXIS<1...99>
assigns axis characteristics from the corresponding AXIS definition to the vertical (y) axis.
See also: AXIS Statement
Featured in: Labeling Contour Lines

VMINOR=number-of-minor-ticks
VM=number-of-minor-ticks
specifies the number of minor tick marks located between each major tick mark on the vertical (y) axis. No values are displayed for minor tick marks. The VMINOR= option overrides the MINOR= option in an AXIS definition that is assigned to the vertical (y) axis.

VREF=value-list
draws one or more reference lines perpendicular to the vertical axis at points specified by value-list. See the LEVELS= option for a description of value-list.

VREVERSE
specifies that the order of the values on the vertical axis be reversed.

XTICKNUM=number-of-ticks
YTICKNUM=number-of-ticks
specify the number of major tick marks located on a plot's x or y axis, respectively. The value of n must be 2 or greater. The defaults are XTICKNUM=5 and YTICKNUM=5.

The MAJOR= or ORDER= option in an AXIS definition that is assigned to the x axis overrides the XTICKNUM= option. The MAJOR= or ORDER= option in an AXIS definition that is assigned to the y axis overrides the YTICKNUM= option.

Autolabel Suboptions

In the AUTOLABEL= option, autolabel-suboptions can be one or more of the suboptions described here.

CHECK=checking-factor | NONE
specifies a collision checking factor that controls collisions between contour label text and other contour lines or other labels. Values can be integers from 0 to 100, inclusive, where 0 provides minimal collision checking and 100 provides maximal collision checking. Fractional values are permitted. The default is CHECK=75.

CHECK=NONE suppresses contour label collision checking and may substantially lessen the time needed to compute the contour graph.

Specifying a checking factor can slow the graph procedure. Generally, CPU time required to fit all the labels increases in direct proportion to the size of the CHECK= number.

MAXHIDE=amount<units>
specifies the maximum amount of contour line that can be hidden by contour labels. The value of amount must be greater than zero.

Valid units are CELLS (horizontal character cell positions), CM (centimeters), IN (inches), or PCT (percentage of the width of the graphics output area). The default is MAXHIDE=100PCT. If you omit units, a unit specification is searched for in this order:

  1. the GUNIT= option in a GOPTIONS statement

  2. the default unit, CELLS.

If you specify units of PCT or CELLS, the MAXHIDE= suboption calculates the amount of contour line that can be hidden based on the width of the graphics output area. For example, if you specify MAXHIDE=50PCT and if the graphics output area is 9 inches wide, the maximum amount of the contour line that can be hidden by labels is 4.5 inches.

This option maintains data integrity. It provides a check for overly small increments in the STEP= option in the SYMBOL statement. Additionally, it can prevent small contours from being significantly hidden even when the value of STEP= is sufficiently large.

REVEAL
specifies that the contour lines are visible through the label text as dashed lines. Line style 33 is used. This option provides a simple way to see all portions of labeled contours and can be used to inspect the label positions with respect to the contour lines. It is primarily used for debugging. Occasionally, single-character contour labels can be placed off center from the clipped portion of the contour line when the contour line is irregular or jagged.

TOLANGLE=angle
specifies the maximum angle (the tolerance angle) between any two adjacent characters of a contour label. The value of angle must be between 1 and 85 degrees, inclusive. The default is TOLANGLE=30. To force contour labels to fall on very smooth sections, specify a small tolerance angle.

Selecting Contour Levels

You can use the LEVELS= option to select the contour levels for your plot. You use LEVELS= values differently, depending on whether you specify the PATTERN option in the PLOT statement.

When you do not use the PATTERN option, the levels represent the intersection of a plane (parallel to the x-y plane at the z value) and the surface formed by the data. That is, if you use the data to create a surface plot with the G3D procedure, the contour lines in a GCONTOUR procedure plot represent the intersection of the plane and the surface.

For example, suppose that you use the G3D procedure, and your data produces a surface plot like the one shown in Surface Plot. The same data used with this PLOT statement in the GCONTOUR procedure produces a contour plot like the one in Line Contour Levels: 

plot y*x=z / levels=-7.5 to 7.5 by 2.5;

The contour lines in Line Contour Levels represent the intersection of the surface in Surface Plot with planes parallel to the plane formed by the variables x and y and located at z values of -7.5, -5.0, -2.5, and so on.

Surface Plot

[IMAGE]

Line Contour Levels

[IMAGE]

When you use the PATTERN option, contour levels are represented by rectangles filled with patterns. The rectangles are formed by points in the x-y grid. The contour pattern of a rectangle, or grid cell, is determined by the mean or average value of the z variable for the four corners of the rectangle. The grid cell is assigned the pattern for the level closest to the calculated mean. For example, if you have specified contour levels of 0, 5, and 10, and the plot contains a grid cell with a mean of 100, it is assigned the pattern for the nearest level: 10. A grid cell with a mean of 7.6 will also be assigned the pattern for the 10 level.

Pattern Contour Levels shows a contour plot with the PATTERN option that uses the same data and contour levels as Line Contour Levels. The pattern for the rectangle is assigned depending on the mean of the grid values at the four corners. As a result, two contour plots using the same contour levels can present your data differently if one plot uses a pattern and the other does not. The contour pattern boundaries do not correspond to the contour lines shown in Line Contour Levels.

Pattern Contour Levels

[IMAGE]

Specifying Axis Order

You can use AXIS statements to modify the text and appearance of plot axes, and then you can assign the axes to the contour plot with the PLOT statement's HAXIS= and VAXIS= options. If the AXIS statement uses an ORDER= option, there are special considerations for using that AXIS definition with the GCONTOUR procedure.

A list of variable values that are specified with the AXIS statement's ORDER= option must contain numbers listed in ascending or descending order; these numbers are treated as a continuous data range for an axis. Thus, for a contour line or pattern to span the entire specified range, it is not necessary for the maximum and minimum values of the list to match exactly with the maximum and minimum data values of the corresponding x or y variable. For example, suppose that you assign this AXIS definition to the horizontal (x) axis: 

axis1 order=-2.5 to 2.5 by .5

Suppose also that the horizontal axis variable has these values: -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5. Depending on the data, contours could extend through the full range of the ORDER= list rather than from -2 to 2, which are the actual values of the variable assigned to the horizontal (x) axis. In this case, values are interpolated for the x variable at any point where the y variable intersects the minimum axis value (-2.5) or the maximum axis value (2.5). Data values that are outside of the axis range (in this case, -5, -4, -3, 3, 4, and 5) are clipped from the plot.

When ORDER= lists cause data clipping, internal plotting grids are modified according to these rules:

In addition, if you assign the following AXIS definition to a plot of the same data, the contour levels on the plot will not extend beyond the range of the data: 

axis1 order=-10 to 10 by 1;

To see the effects of the ORDER= option:

Effects of the AXIS Statement's ORDER= Option: ORDER= values match variable values

[IMAGE]

Effects of the AXIS Statement's ORDER= Option: ORDER= range is smaller than variable range

[IMAGE]

Effects of the AXIS Statement's ORDER= Option: ORDER= range is larger than variable range

[IMAGE]

Modifying Contour Lines and Labels with the SYMBOL Statement

When you use the AUTOLABEL option, the LLEVELS= and CLEVELS= options are ignored, and contour-line and label attributes are controlled by the SYMBOL statement. Defaults are used if not enough SYMBOL statements are specified to match the number of contour levels.

If a SYMBOL statement does not include a color option, that statement may be applied to more than one contour level. In this case, the SYMBOL statement is used once with every color in the colors list and generates more than one SYMBOL definition. See SYMBOL Statement for details.

The Effect of SYMBOL Statement Options on Contour Lines and Labels describes how SYMBOL statement options affect contour plot lines and labels.

The Effect of SYMBOL Statement Options on Contour Lines and Labels
SYMBOL Statement Option Contour Line or Label Element Affected
LINE=line-type
 Contour line style
WIDTH=n
 Contour line thickness
CI=line-color or COLOR=color
 Contour line color
FONT=font
 Contour label font
HEIGHT=height
 Contour label height
CV=color or COLOR=color
 Contour label color
STEP=distance<units> Minimum distance between labels on the same contour line
VALUE='text' Contour label text
VALUE=NONE Suppresses the contour label text

The SYMBOL statement option INTERPOL= is not supported by the GCONTOUR procedure.

The STEP= option specifies the minimum distance between contour labels. The lower the value, the more labels the procedure uses. A STEP= value of less than 10 percent is ignored by the GCONTOUR procedure and a value of 10 percent is substituted.

See STEP= for more information.

Specifying Text for Contour Labels

To override the default labels that are displayed by the AUTOLABEL option, you can specify label text for one or more contour lines. To do so, use both the FONT= and VALUE= options on the SYMBOL statement that is assigned to the contour level. Default labels are used for contour levels that you do not label.

For example, this SYMBOL1 statement displays the text string Highest in the Swiss font on the contour line that it modifies: 

symbol1 font=swiss value='Highest';

You must specify both FONT= and VALUE= or the text is not used. For an example, see Labeling Contour Lines.


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Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.