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

Bivariate, Color Symbolization

For color (hue or hue/intensity) based bivariate mapping, a point symbol should be selected from the available marker sets (PLOTTER, COLOR, MINERAL, MUNICIPAL, OILGAS, TEMPLATE, USGS, or WATER); these markersets are displayed in Appendix B of the Map Display and Query guide. The color specification of that point symbol will then be changed to show variations in data and meta-data. For size and hue based maps, only a sets of hues must be chosen; symbol size and shape is calculated by ARC/INFO.

Two Nominal Data Sets--Shape and Hue

This macro (PSH.aml) uses two lookup tables for symbolizing two nominal data sets. Unlike shape and orientation, neither shape or hue is, in general, the dominant visual variable. Visual hierarchies can be established by selecting intense color and similar shapes--this will make color hue the more prominent of the two nominal visual variables. See Figure 3.4a.

PSH <shape_lookup> <hue_lookup> {markerset} {markersize} {value} {saturation}

<shape_lookup>

specifies marker symbol numbers

<hue_lookup>

specifies HLS hue data (values of 0 to 360)

{markerset}

a markerset for shapes--defaults to the current markerset

{markersize}

a size for the markers--defaults to 0.15 inches

{value} {saturation}

defaults of 50 and 100 (maximum intensity)

Two Nominal Data Sets--Dual Hue Ranges

Color hue is best used for nominal data, although with well selected colors, hue can be used with ordinal data. Use of the spectral encoding bivariate mapping scheme requires careful selection of colors. For the specification of colors for dual-hue range mapping, the CMY (Cyan, Yellow, Magenta) color scheme is most useful. A color chart for this color specification system is in Appendix J of the Map Display and Query manual. For a four by four color matrix, color specifications like the following can be used:

Cyan	100	Cyan	100	Cyan	100	Cyan	100
Magenta	0	Magenta	33	Magenta	67	Magenta	100
Cyan	67	Cyan	67	Cyan	67	Cyan	67
Magenta	0	Magenta	33	Magenta	67	Magenta	100
Cyan	33	Cyan	33	Cyan	33	Cyan	33
Magenta	0	Magenta	33	Magenta	67	Magenta	100
Cyan	0	Cyan	0	Cyan	0	Cyan	0
Magenta	0	Magenta	33	Magenta	67	Magenta	100

This pattern can be generated with SETAUTO.aml with the command line 0 33. Yellow should be held constant for each of the sixteen positions--generally, 100 should be good. Even with this control of changes in color, dual-hue range maps should generally be used only for nominal data--the complementary-color system tends to present ordinal data better. See Figure 3.4b and PDH.aml.

PDH <yellow-green_lookup> <yellow-red_lookup> {markerset} {markersymbol} {markersize}

<yellow-green_lookup>

specifies changes in cyan (values of 0 to 100)

<yellow-red_lookup>

specifies changes in magenta (values of 0 to 100)

{markerset} {markersymbol}

specify which symbol will be drawn with--defaults to current

{markersize}

silicifies the size of the marker--defaults to 0.15 inches.

Two Ordinal Data Sets--Complementary Colors

This AML is a variation on the previous macro. The change is in the colors used to symbolize data; complementary colors are hues that are on opposite sides of the Munsell or Tektronix color spaces and mix to form grey. This mixing allows highlighting of data that is not highly correlated, because these areas will appear in color, whereas the central axis of correlated data will appear in grey. This method allows the representation of both positive and negative correlations; negative correlations should be represented by reversing the values in one of the lookup tables--this changes the direction of the slope of the central axis. Note that white should be avoided because the entire symbol will disappear on a white sheet of paper; use a range from 5 to 100 for percent area inked. See Figure 3.4c and PCC.aml.

PCC <cyan_lookup> <red_lookup> {markerset} {markersymbol} {markersize}

<cyan_lookup>

specifies changes in cyan (values from 0 to 100)

<red_lookup>

specifies changes in red (values from 0 to 100)

{markerset} {markersymbol}

specify which symbol will be drawn with--defaults to current

{markersize}

specifies the size of the marker--defaults to 0.15 inches.

Point Legend Creation

Although the usage of this AML (PBL.aml) is lengthy, it allows one macro to generate a bivariate legend for three different types of point symbolization schemes: dual hue, complementary colors, and hue and intensity. See Figure 3.4d for both dual-hue and complementary-color legends and Figure 3.5b for a hue and intensity legend.

PBL <data1_lookup> <data2_lookup> <start_x> <start_y> <step_x> <step_y> <d|c|h>
{markerset} {markersymbol} {markersize} {textset} {font} {point} {decimal_precision}

<data1_lookup>

the first lookup given in one of the bivariate AMLs

<data2_lookup>

the second lookup given in one of the bivariate AMLs

<start_x> <start_y>

the lower left corner of the legend matrix, in PAGEUNITS

<step_x> <step_y>

the separation of symbols on the x and y axes, in PAGEUNITS

{markerset} {markersymbol}

specify which symbol will be drawn with--defaults to current

{markersize}

specifies the size of the marker--defaults to 0.15 inches

{textset} {font} {point}

specify a textset for legend labels--defaults to a roman, 10 point

{decimal_precision}

number of decimal places shown for ratio data labels--defaults to 2.

Nominal Data, and Ordinal Data--Hue and Intensity

Color hue is best used for nominal data; color intensity, on the other hand, is best used for ordinal data (and generally only for meta-data, not a second data variable). This color scheme represents meta-data better than the dual-hue and complementary-color bivariate systems, because the data variable is clearly displayed in a constant hue, unlike the other color bivariate methods. See Figure 3.5a and PHI.aml.

PHI <hue_lookup> <intensity_lookup> {markerset} {markersymbol} {markersize}

<hue_lookup>

specifies changes in HLS hue (from 0 to 360)

<intensity_lookup>

specifies changes in HLS saturation (from 0 to 100)

{markerset} {markersymbol}

specify which symbol will be drawn with--defaults to current

{markersize}

specifies the size of the marker--defaults to 0.15 inches.

Two Ratio Data Sets--Equiprobability Ellipse

Eyton's ellipse is a variation on the complementary color system. The colors that are used are the same, but the linear correlation between the two variables is used to determine a central category, which specifically highlights correlation. This AML requires that the EYTON.aml, presented in chapter two, be run first. See Figures 3.5c and on 5.7b for a legend display, and PEE.aml.

PEE <ellipse_lookup> {markerset} {markersymbol} {markersize}

<ellipse_lookup>

a lookup table generated by EYTON.aml

{markerset} {markersymbol}

specify which symbol will be drawn with--defaults to current

{markersize}

specifies the size of the marker--defaults to 0.15 inches.

Ratio Data, and Nominal Data--Size and Hue

This macro is the color equivalent of the one that generated Figure 3.3d. Unlike that AML though, this should be used for one nominal data variable and one ratio data variable. See Figure 3.5d and PCH.aml.

PCH <size_item> <hue_lookup> {minimum_size} {maximum_size} {value} {intensity}

<size_item>

a numeric data item of the coverage reference by <hue_lookup>

<hue_lookup>

specifies changes in HLS hue (from 0 to 360)

{minimum_size}

graduated circle size for the smallest data value--default = 0.05 inches

{maximum_size}

graduated circle size for the largest data value--default = 0.5 inches

{value} {intensity}

default to 50 and 100 (maximum intensity).