• 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

Multivariate Symbolization

Multivariate line symbolization allows the representation of three or more variables about the same line segment on the same map. This is useful for the communication of spatial patterns, but--as with all bi- and multivariate maps--legends should include explanations of the data representation technique.

Three Ordinal to Ratio Data Sets--Red, Green and Blue Symbolization

For representing three ratio data values, line color can be specified by control of the red, green and blue (or cyan, magenta and yellow) components of the color additive (or subtractive) process. This use of RGB color is similar to that used to display satellite imagery. As such, the AML LRGB.aml requires three numeric data items, which are linearly stretched from 0 to 250 (this prevents white lines on white paper). See Figure 4.5a.

LRGB <cover> <red_item> <green_item> <blue_item> {linesize} {r|c} {arc|route|section} {subclass}

<cover>

the coverage to be displayed

<red_item> <green_item> <blue_item>

three numeric data fields in <cover>

{linesize}

specifies a line width--default is 0.1 inches

{r|c}

specifies the RGB or CMY color model

{arc|route|section} {subclass}

specifies arcs (default) or route/section and subclass.

Nominal Data, Ratio Data, and Nominal Data--Shape, Size and Hue

By adding a ratio variable to the bivariate representation shown in Figure 4.3a, a trivariate representation results. This allow communication of two nominal variables, and a third, ratio, variable. The AML requires two lookup tables: one that relates nominal data to line symbols; the other relating nominal data to HLS hue (0 to 300). The size information is generated directly from a numeric item in the arc (or route or section) attribute table. See Figure 4.5b, the discussion of size on page 50 and LHSZ.aml.

LSHZ <shape_lookup> <hue_lookup> <size_item> {lineset}
{size_exponent} {size_factor} {minimum_size} {value} {intensity}

<shape_lookup>

specifies line symbol numbers

<hue_lookup>

specifies HLS hues

<size_item>

a ratio data field in the attribute table referenced by <shape_lookup>

{lineset}

specifies a lineset for shapes--defaults to current lineset

{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, Ratio Data, and Ordinal Data--Shape, Size and Value

This AML is addition of the bivariate representation techniques shown in Figure 4.2b, Figure 4.2c and Figure 4.2d. This monochrome, trivariate mapping system allows representation of nominal data and ratio data, along with an ordinal data set, which can be used for representing the ratio data set's meta-data. The AML requires the two lookup tables: one for relating nominal data to line symbols; the other for relating ordinal data to HLS value (0--black to 80--almost white). The size of the line symbol is generated from a numeric data item in an attribute table. See Figure 4.5c and LSZV.aml.

LSZV <shape_lookup> <size_item> <value_lookup> {lineset}
{size_exponent} {size_factor} {minimum_size} {hue} {intensity}

<shape_lookup>

specifies line symbol numbers

<size_item>

a ratio data field in the attribute table referenced by <shape_lookup>

<value_lookup>

specifies HLS lightness

{lineset}

specifies a lineset for shapes--defaults to current lineset

{size_exponent} {size_factor} {minimum_size}

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

{hue} {intensity}

specify a color to be value shaded.

Ratio Data, Nominal Data, and Ordinal Data--Size, Hue and Intensity

As with the previous AML, this macro is displays a nominal data set (with hue instead of shape) and a ratio data set, along with an ordinal data set, which can be used for representing the ratio data's meta-data. The AML requires two lookup tables: for nominal data, a table of HLS hues (0 to 300); for ordinal data, a table of HLS saturation (20--off gray to 100--maximum intensity). The line symbol size is calculated from a numeric item in the attribute table specified in the second lookup table. See Figure 4.5d and LHIZ.aml.

LHIZ <hue_lookup> <intensity_lookup> <size_item> {size_exponent} {size_factor} {minimum_size}

<hue_lookup>

specifies HLS hue

<intensity_lookup>

specifies HLS saturation

<size_item>

a ratio data field in the attribute table referenced by <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.