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

Monovariate Symbolization

The two primary methods of surface display, isolines and fishnets, display a single variable by control of location. This should only be used for interval or ratio data.

Ratio Data--Isoline Location

Figure 9.1a: SISO.aml A continuous, smoothly changing ratio surface displayed with isolines. The AMl attempts to place contour labels along the lines.

Isoline coverages are arc coverages that can be labeled with a surface height (although elevation is a common use, it is not the only use of isolines and fishnets). SISO.aml draws arcs with the current line type and labels the arcs. Because the current line type is used multivariate maps can be created by changing line hue, value, shape, etc. See Figure 9.1a.

SISO <cover> {contour_item} {textset} {font} {point_size} {float_precision}

<cover>

a coverage generated by POLYCONT

{contour_item}

defaults to the item generated by POLYCONT (contour)

{textset} {font} {point_size}

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

{float_precision}

the number of decimal places shown in contour labels--defaults to 0.

Ratio Data--Fishnet Height

Figure 9.1b: SF.aml Ratio are data displayed with a fishnet. This display shows the default options of SURFACEDEFAULTS and the AML.

The macro, SF.aml, simply automates the default setup of a surface display, calculates a better `Z' expansion value than ARCPLOT, and displays the surface. The expansion value relates the data values used to describe X and Y locations with the value used to describe the height at a location. For example, the default view for a surface could appear absolutely flat, if the X and Y coordinates have a much larger range than the Z values. See Figure 9.1b.

SF <surface> {zfactor} {lattice|tin} {resolution}

<surface>

a grid layer or a TIN

{zfactor}

`Z' expansion factor--defaults to range_of_z / the larger of x_range and y_range

{lattice|tin}

the type of <surface>--defaults to lattice (grid)

{resolution}

the density of fishnet lines--defaults to the SURFACEDEFAULTS value.

Isoline and Fishnet Legends

Figure 9.1d: SFL.aml A legend for the surface in figure 9.1b. Because of the comparative abstractness of isolines, legends for both fishnets and isolines should show a labeled surface.

Isoline and fishnet legends can be generated by specifying a small area for the display of a fishnet that has isolines drawn on it, and labeled. This is most beneficial for isoline maps, which can be greatly enhanced by the inclusion of the less abstract fishnet as the legend. See SFL.aml and Figure 9.1d.

SFL <surface> <x_start> <y_start> <x_size> <y_size> <contour_interval> {zscale} {lattice|tin}
{textset} {font} {point} {precision}

<surface>

a grid layer or a TIN--not an isoline (arc) coverage

<x_start> <y_start>

the lower left corner of the legend

<x_size> <y_size>

the size of the legend drawing area

<contour_interval>

the separation distance in Z of isolines

{zscale}

a `Z' expansion factor

{lattice|tin}

the type of <surface>--defaults to lattice

{textset} {font} {point}

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

{precision}

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