• Introduction
• The Utility of Maps
• Producing Displays
• Point Symbolization
• Line Symbolization
  • Monovariate
  • Bivariate Color
  • Multivariate
• Choropleth Symbolization
• Graduated Symbol
• Grid Symbolization
• Dot Density Symbolization
• Isopleth Symbolization
• Thematic Mapping
• References
• Index
• Author Index
• Symbol Index
• Site Map

Bivariate, Color Symbolization

Color hue and intensity add two important visual variables to the representational techniques possible in ARC/INFO. Hue allows better specification of nominal variables than texture (particularly in monochrome, bivariate mapping) and can also be used for ordinal data. Intensity is useful for display of uncertainty meta-data.

Two Nominal Data Sets--Texture or Shape, and Hue

Figure 4.3a: LSH.aml Two nominal data sets displayed with shape and hue.

This AML (LSH.aml) takes advantage of the ability of shape to convey nominal data, and it uses color hue to specify a second nominal category. The AML requires a lookup table that specifies line symbols for the shape (or texture) variable, and a second AML that specifies HLS hue values (0 to 300). See Figure 4.3a.

LSH <shape_lookup> <hue_lookup> {lineset} {linesize} {value} {intensity}

<shape_lookup>

specifies line symbol numbers

<hue_lookup>

specifies HLS hue data

{lineset}

select a lineset for shapes--defaults to the current lineset;
{linesize}

specifies a line width--defaults to 0.1 inches

{value} {intensity}

defaults: 50, 100 (maximum brightness).

Two Nominal Data Sets--Dual Hue Ranges

Figure 4.3b: LDH.aml Two nominal data sets displayed with the dual-hue range technique. Note the lack of discrenable order in color changes--this necessitates a legend (below).

Another method of displaying two nominal data sets is the dual-hue range technique. This uses two hue ranges (yellow to red and yellow to green) to specify data values. The combination of the two color ranges results in unique colors for each combination of data values. The AML requires two lookup tables, which specify color for the CMY color model (ranges of 0 to 100). See Figure 4.3b and LDH.aml.

LDH <yellow-green_lookup> <yellow-red_lookup> {linesize}

<yellow-green_lookup>

specifies changes in cyan (from 0 to 100)

<yellow-red_lookup>

specifies changes in magenta (from 0 to 100)

{linesize}

specifies a line width--defaults to 0.1 inches.

Two Ordinal Data Sets--Complementary Colors

Figure 4.3c: LCC.aml Two ordinal data sets displayed with the complementary color technique. this method highlights correlation better than dual-hue mapping.

The use of color to specify ordinal data requires careful selection of colors. By use of color intensity in two complementary colors (equal amounts of each yield gray), it is possible to specify a color system that represents ordinal information well. This AML (LCC.aml) accomplishes this with two lookup tables for the CMY color system (color numbers of 10 to 100), one of which is used for cyan and the other is used for magenta and yellow, together (this yields red). A central diagonal results, which is gray. With color values based directly on data values, this gray line would represent linear correlation between the two variables. See Figure 4.3c.

LCC <cyan_lookup> <red_lookup> {linesize}

<cyan_lookup>

specifies changes in cyan

<red_lookup>

specifies changes in red

{linesize}

specifies a line width--defaults to 0.1 inches.

Bivariate Color Legends

Figure 4.3d: LBL.aml Dual-hue (above) and complementary color legends. Note the central gray diagonal in the complementary color legend.

Legends should present the map reader with as much information as possible. This AML not only generates a line symbol for each color bivariate scheme, but also labels the rows and columns with the appropriate name or data range and provides the total number of items in each row or column. See Figure 4.3d, Figure 4.4d and LBL.aml.

LBL <lookup_1> <lookup_2> <start_x> <start_y> <step_x> <step_y> <d|c|h> {linesize} {textset} {font} {point} {floating_point_precision}

<lookup_1>

the first lookup specified in LDH, LHI or LCC

<lookup_2>

the second lookup table from on of the display AMLs

the lower left corner of the legend

<step_x> <step_y>

the size of each row and column

<d|c|h>

the symbolization method: Dual hue, Complementary color, or Hue and intensity

{linesize}

specifies a line width--defaults to 0.1 inches

{textset} {font} {point}

define the labelling text--defaults to a 10 point roman font

{floating_point_precision}

the number of decimal places to be shown--the default is 2.

Two Ratio Data Sets--Eyton's Ellipse for Lines

Figure 4.4a: LEE.aml Two ratio data sets displayed with an equiprobability elipse. This selects the central cluster of correlated data as a fifth category in a 2x2 matrix.

A development of the complementary color system that specifically highlights correlation is Eyton's equiprobability ellipse. This system calculates the correlation between two ratio variables and specifies a complementary color shade to each data pair. The central category contains the central cluster of correlated data. This system requires that the AML described in chapter two be run to determine the classification. Once this is done, this AML (LEE.aml) displays linear data. See Figure 4.4a.

LEE <ellipse_lookup> {lineset} {linesymbol} {linesize}

<ellipse_lookup>

a lookup table for linear data created by EYTON.aml

{lineset} {linesymbol}

define a line to use for shading--defaults to the current line

{linesize}

specifies a line width--defaults to 0.1 inches.

Ratio Data, and Nominal Data--Size and Hue

Figure 4.4b: LHZ.aml A nominal data set displayed with hue and a ratio data set displayed with size.

For combinations of nominal and ratio data, shape (which can be used in monochrome maps) or hue can be used to specify the nominal data and size can be used to display the ratio information. This AML uses a lookup table that relates nominal data to HLS color hue (0 to 300) and a numeric item in the coverage's attribute table. See Figure 4.4b and LHZ.aml.

LHZ <hue_lookup> <size_item> {size_exponent} {size_factor} {minimum_size} {value} {intensity}

<hue_lookup>

specifies HLS hues

<size_item>

a numeric data item in the attribute table referred to be <hue_lookup>

{size_exponent} {size_factor} {minimum_size}

define the scaling of sizes,
defaults: size_exponent = 1; size_factor = 0.15; minimum_size = 0.02 inches

{value} {intensity}

default to 50 and 100--maximum intensity.

Nominal Data and Ordinal Meta-Data--Hue and Intensity

Figure 4.4c: LHI.aml A nominal data set displayed with hue and an ordinal data set displayed with intensity. Intense colors tend to stand out in an image, and can highlight certain data.

Figure 4.4d: LBL.aml Hue and intensity legend. Note the lack of a diagonal, as in the complementary color system; this makes hue and intensity better suited to data and meta-data.

For display of a nominal data and meta-data, color hue can be used for the nominal information and color intensity can be used for the meta-data. This AML (LHI.aml) requires a lookup table for relating nominal data to HLS hue (0 to 300) and a second table for relating meta-data to HLS saturation (20 to 100). See Figure 4.4c.

LHI <hue_lookup> <intensity_lookup> {linesize}

<hue_lookup>

specifies HLS hue

<intensity_lookup>

specifies HLS saturation

{linesize}

specifies a line width--default is 0.1 inches.