Monochrome, Bivariate Symbolization
Symbol size is good for either ordinal or interval/ratio data. For the generation of value-shaded, graduated symbol maps (which should be used for discrete, abruptly changing, ordinal to ratio area data and meta-data), size must be used in conjunction with SHADECOLOR. This combination allows the display of either data and meta-data, or two data variables.
Ordinal to Ratio Data, and Ordinal Data--Graduated Circles and Value
Figure 6.1c: GCV.aml Graduated circles that are value shaded with an ordinal data set. This is best used for meta-data, although a second data set can be displayed as well.
This AML (GCV.aml) develops the display of graduated circles to include the value shading of the circle. The value_lookup must specify lightness data in the HLS color model, with value ranging from 0 black to no more than 90 (light gray), in order to avoid white symbols on a white background. See Figure 6.1c.
GCV <size_item> <value_lookup>
{minimum_size} {maximum_size} {hue} {saturation}
<size_item>- a numeric data field in the attribute table referred to by <value_lookup>
<value_lookup>- specifies HLS lightness data
{minimum_size} {maximum_size}- the minimum and maximum circle sizes, the defaults are 0.05 and 0.5 inches
{hue} {saturation}- specify a color that will be value shaded.
Ordinal to Ratio Data, and Ordinal Data--Cartograms Shaded by Value
Figure 6.1d: GGV.aml Value shaded cartograms. The size data is the same as figure 6.1b, but here the scaling exponent is 0.5; this represents smaller data values with larger polygons.
By using interactive map composition, cartograms (use of scaled areas to represent a data value) can be drawn in ARC/INFO. Value is used to represent a second variable; this can be used for a second variable when color is not an available option, or meta-data. See Figure 6.1d and GGV.aml.
GGV <size_item> <value_lookup>
{scale_factor} {hue} {intensity}
<size_item>- a numeric data field in the attribute table referred to by <value_lookup>
<value_lookup>- specifies HLS lightness data
{scale_factor}- specifies the exponent used to calculated cartogram size--defaults to 1
{hue} {intensity}- specify a color that will be value shaded.