Multivariate Symbolization
Two multivariate symbolization methods are presented here. Hue, intensity and size is a development of hue and size. Graduated pie symbols allow the display of a total value and a set of components of that value.
Ratio Data, Nominal Data, and Ordinal Data--Circles, Hue and Intensity
Figure 6.3a: GCHI.aml Graduated circles shaded with color hue (a nominal data set) and intensity (an ordinal data set).
Like all graduated symbols, size should be used to represent a ratio variable (that is discrete and abruptly changing). Hue can be used to represent a second, nominal variable, and intensity can be used to represent an ordinal data--including ratio meta-data. See Figure 6.3a and GCHI.aml.
GCHI <size_item> <hue_lookup>
<intensity_lookup> {minimum_size}
{maximum_size}
<size_item>- a numeric data field in the cover referred to by <hue_lookup>
<hue_lookup>- specifies HLS hue (from 0 to 300)
<intensity_lookup>- specifies HLS saturation (from 20 to 100)
{minimum_size}- the size representing the smallest data value--defaults to 0.05 inches
{maximum_size}- the size representing the largest data value--defaults to 0.5 inches.
Ratio Data, Nominal Data, and Ordinal Data--Cartograms, Hue and Intensity
Figure 6.3b: GGHI.aml Cartograms shaded with hue and intensity. Cartograms should be used to represent density data.
Like the previous AML, this macro should be used to represent a ratio data set, a nominal data set, and an ordinal data set (which can be ratio meta-data). Like the other cartogram AML's this should be used to display density information. See Figure 6.3b and GGHI.aml.
GGHI <size_item> <hue_lookup>
<intensity_lookup> {size_scale}
<size_item>- a numeric data filed in the coverage referred to by <hue_lookup>
<hue_lookup>- specifies HLS hue data (from 0 to 300)
<intensity_lookup>- specifies HLS saturation (from 20 to 100)
{size_scale}- specifies the exponent used to calculate cartogram size--defaults to 1.
Ratio Data--Polygon Pie Graphs
Figure 6.3c: GP.aml Graduated pie symbols. These show a total value (size) and the components of the total (each pie wedge).
In addition to the appropriate spatial characteristics, graduated pie maps should also have a data value that represents a total of multiple elements (this total determines circle size). Each element displayed a fraction (pie wedge) of the whole. The AML automatically determines hues for each element. See Figure 6.3c and GP.aml.
GP <cover> <size_item>
<minimum_size> <maximum_size>
<number_of_subitems>
<item_1...item_n>
<cover>- a polygon coverage with data that is discontinuous and abruptly changing
<size_item>- a numeric field in the attribute table of <cover>, which is a total of <items>
<minimum_size>- the size of the smallest data value's circle (0.05 may be good)
<maximum_size>- the size of the largest data value's circle (0.5 may be good)
<number_of_subitems>- the total number of items given in <item_1...item_n>
<item_1...item_n>- numeric fields in <cover> that represent elements of <size_item>.
Graduated Pie Legends
Figure 6.3d: GPL.aml A legend for figure 6.3c. The size data can be displayed with the graduated circle legend AML. Pie slices are shaded and labeled by this AML.
Legends for graduated pie can be generated by using the graduated circle legend AML for displaying size data, and using GPL.aml to display the hues used to shade pie slices. This AML uses the same hue selection routine as the graduated pie mapping AMLs, but it only draws one circle with equally sized pie slices. See Figure 6.3d.
GPL <pie_size> <center_x>
<center_y> <number_of_data_items> {textset}
{font} {point_size} {data_item_names}
<pie_size>- a numeric value in PAGEUNITS for the circle radius
<center_x> <center_y>- the center location of the circle
<number_of_data_items>- the <number_of_items> used in the mapping AML
{textset} {font} {point_size}- define the labelling text--defaults to a 10 point roman font
{data_item_names}- the labelling text--if used, there should be <number_of_data_items> separated by spaces.