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

Color, Bivariate Symbolization

Symbol size is good for either ordinal or interval/ratio data. Graduated symbol maps should be used for discrete, abruptly changing, ordinal to ratio area data. Color hue can be used to display a second, nominal data set.

Ordinal to Ratio Data, and Nominal Data--Graduated Circles and Hue

Unlike the macro used to generate Figure 6.1c, this AML should be used for two data sets--one ratio and one nominal, rather than data and meta-data. See Figure 6.2a and GCH.aml.

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

<size_item>

a numeric data field in attribute table referred to by <hue_lookup>

<hue_lookup>

specifies HLS hue data (from 0 to 360)

{minimum_size}

the size of the smallest data value's circle--defaults to 0.05 inches

{maximum_size}

the size of the largest data value's circle--defaults to 0.5 inches

{value} {intensity}

default to 50 and 100 (maximum intensity).

Graduated Circle Legends

This AML (GCL.aml) generates a series of circles that are labeled with the data value represented by that size, and filled with the polygon fill in shadesymbol 1. It works for all of the graduated symbol AMLs (point and area). It should be supplemented by an additional figure if the circles are hue or value shaded (see Figure 6.2b).

GCL <cover> <point|node|poly> <size_item> <start_x> <start_y> <number_of_symbols>
{minimum_size} {maximum_size} {textset} {font} {point} {float_precision}

<cover>

the coverage that was displayed with graduated circles

<point|node|poly>

the type of <cover>

<size_item>

the numeric data item in the attribute table of <cover>

<start_x> <start_y>

lower center of the column of circles

<number_of_symbols>

the number of circle to be drawn for the legend

{minimum_size}

the size used to display the smallest data value--defaults to 0.05 inches

{maximum_size}

the size used to display the largest data value--defaults to 0.5 inches

{textset} {font} {point}

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

{float_precision}

the number of decimal places to be shown--defaults to 2.

Ordinal to Ratio Data, and Nominal Data--Cartograms with Hue

This AML should be used to display a nominal data set, along with density data. See Figure 6.2c and GGH.aml.

GGH <size_item> <hue_lookup> {value} {intensity} {size_scale}

<size_item>

a numeric data field in the attribute table referred to by <hue_lookup>

<hue_lookup>

specifies HLS hue (from 0 to 300)

{value} {intensity}

default to 50 and 100 (maximum intensity)

{size_scale}

specifies the exponent used to calculate cartogram size--defaults to 1.

Cartogram Legends

This AML, like the graduated circle legend AML, generates a series of polygons that represent data values. Each polygon is placed inside an unscaled outline of the polygon, and labeled. The polygon is drawn with the current polygon shade fill. This legend must also be supplemented by a legend specifying hue, value, or hue and intensity, if more than one variable is shown on the map (see Figure 6.2d).

GGL <cover> <size_item> <start_x> <start_y> <size_x> <size_y> <number_of_symbols
{scale} {polygon} {textset} {font} {point} {precision}

<cover>

the polygon coverage displayed with cartograms

<size_item>

a numeric data field in the attribute table of <cover>

<start_x> <start_y>

the lower left corner of the legend area

<size_x> <size_y>

the drawing size of each polygon

<number_of_symbols>

the total number of legend symbols

{scale}

the exponent used to calculate cartogram size--defaults to 1

{polygon}

the record number of an example polygon--defaults to the middle record

{textset} {font} {point}

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

{precision}

the number of decimal places to be shown--defaults to 4.