Chapter 8

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Production of dot density maps, which should be used for discrete, smoothly changing area data, in ARC/INFO requires the use of GRID and TIN for their creation. This is accomplished by converting a polygon coverage to a grid data layer; if necessary, smoothing the resulting grid; then converting the grid into a stepped surface polygon coverage. ARCPLOT then fills the polygons with dots.

Conversion of Polygons to Dot Density

POLYDOT.aml performs the conversion from polygons based on choropleth boundaries to polygons based on stepped surface boundaries. A lookup table for the input coverage is used to determine the steps. The lookup table can be based on Jenks optimal, or some other classification method. The AML modifies this input lookup table, in order to make it the lookup table for the output coverage. See the discussion of surface generation on page 84.

POLYDOT <lookup_table> <out_cover> {resolution} {i|s|t}

<lookup_table>
specifies a stepped surface classification for <out_cover>
<out_cover>
the resulting stepped surface coverage
{resolution}
the grid cell size for creating a surface, defaults to one hundredth of the smallest axis of the <lookup_table> coverage
{i|s|t}
the method of creating the surface: Idw, Spline, or Trend