Bivariate, Monochrome Symbolization
Most of the AML's presented in this section make use of shape to indicate a nominal distinction. An appropriate symbol set should be selected (or created) and one of the bivariate methods should be selected on the basis of the second variable's type.
Two Nominal Data Sets--Shape and Orientation
Figure 3.3a: PSO.aml Two nominal data sets displayed with shape (primary data) and orientation (secondary data).
For nominal data and meta-data, shape and orientation can be combined to create bivariate point symbolization. Shape should generally be used for the primary data, and orientation for the less important data, or meta-data (varying orientations of the same shape seem to 'go together' more than the same orientation of varying shapes). PSO.aml, uses lookup tables for both shape and orientation to generate a bivariate display; see Figure 3.3a. Note that this AML (as with all that follow) require that any necessary lookup tables be set up in the format generated by SETMAN.aml and JENKS.aml prior to running this routine.
PSO <shape_lookup>
<orientation_lookup> {markerset}
{markersize}
<shape_lookup>- specifies marker symbol numbers
<orientation_lookup>- specifies angles in degrees
{markerset}- a markerset for shapes--defaults to the current markerset
{markersize}- a size for the markers--defaults to 0.15 inches
Nominal Data, and Ordinal Data--Shape and Value
Figure 3.3b: PSV.aml A Nominal data displayed with shape and an ordinal data set displayed with value. This is better for meta-data than a second data set.
As with the next AML, this routine uses nominal primary data and ordinal secondary data, but the visual hierarchy established by value makes it more appropriate for display of meta-data than size. With value, uncertain values of the primary data can be faded into the background; see Figure 3.3b and PSV.aml.
PSV <shape_lookup> <value_lookup>
{markerset} {markersize} {hue} {intensity}
<shape_lookup>- specifies marker symbol numbers
<value_lookup>- specifies HLS lightness data (0 to 100)
{markerset}- a markerset for shapes--defaults to the current markerset
{markersize}- a size for the markers--defaults to 0.15 inches
{hue} {intensity}- specify a color that will be value shaded.
Nominal Data, and Ratio Data--Shape and Size
Figure 3.3c: PSZ.aml A nominal data set displayed with shape and a ratio data set displayed with size. This is more effective than value for a second data set.
For nominal primary data, shape can be used in conjunction with size to create bivariate point symbols. This seems to work better for two data sets rather than data and meta-data, which should be shown with shape and value; see Figure 3.3c and PSZ.aml (and the size discussion on page 39).
PSZ <shape_lookup> <size_item>
{markerset} {size_exponent} {size_factor}
{minimum_size}
<shape_lookup>- specifies marker symbol numbers
<size_item>- an interval or ratio data item in the coverage named by <shape_lookup>
{markerset}- a markerset for shapes--defaults to the current markerset
{size_exponent} {size_factor} {minimum_size}- define the scaling of sizes,
defaults: size_exponent = 1; size_factor = 0.15; minimum_size = 0.02 inches.
Ratio Data, and Ordinal Data--Size and Value
Figure 3.3d: PCV.aml Interval/Ratio data displayed with graduated circles that are value shaded on the basis of an ordinal data set.
Symbol size and value are good for either ordinal or interval/ratio data. The AML, PCV.aml, combines the two; see Figure 3.3d. Because symbol size is calculated directly from the Point Attribute Table, only one lookup table is needed, but rather than containing point symbol numbers, it should contain color value (0--100) numbers. This system can be used to represent a ratio data value with size, and a meta-data estimate of accuracy with value.
PCV <size_item> <value_lookup>
{minimum_size} {maximum_size} {hue} {intensity}
<size_item>- a numeric item in the coverage referenced by <value_lookup>
<value_lookup>- specifies HLS lightness data
{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
{hue} {intensity}- specify a color that will be value shaded.