Monovariate Symbolization
For single variable dot density maps, the visual variable of texture is used to show changes in data value. By controlling the number of dots placed in an area, data that is discrete, but smoothly changing can be represented.
Ordinal to Ratio Data--Texture
Figure 8.1a: DD.aml Discontinuous and smoothly changing data displayed with dot density. This use of texture is accomplished by converting polygons in to stepped surfaces.
Texture can be controlled by using SHADESEPARATION with shadetype RANDOMDOTS. Higher values should be represented with a small separation--this will increase the dot density. Because of ARCPLOT's dot placement routine, the shade separation for dots of 0 size must not be greater than 4/100 of an inch. For four classes, SETAUTO.aml can be run with the arguments 0 100 0.5 22. See Figure 8.1a and DD.aml.
DD <lookup_table> {dot_size}
<lookup_table>- specifies dot separation in hundredths of PAGEUNITS
{dot_size}- the size of individual dots--defaults to 0.02 inches.
Monovariate Dot Density Legends.
Figure 8.1b: DDL.aml A legend for figure 8.1a. The continuous nature of the data is displayed by the unbroken column and labels at transition points.
Legends for dot density maps must convey the idea of a continuous range of data values. To accomplish this, DDL.aml generates a column that is subdivided, and labeled, at the surface breakpoints, and filled with dots of the appropriate density. See Figure 8.1b.
DDL <dot_lookup> <start_x>
<start_y> <size_x> <size_y> {dot_size}
{textset} {font} {point_size}
{float_precisiont}
<dot_lookup>- the lookup table that specifies shade separations
<start_x> <start_y>- the lower left corner of the legend column
<size_x> <size_y>- the x and y sizes of the legend
{dot_size}- the size of dot used in the map--defaults to 0.02 inches
{textset} {font} {point_size}- define the labelling text--defaults to a 10 point roman font
{float_precision}- the number of decimal places shown in the legend--defaults to 2.