Lucille T. Nowell.
  <i><b>Graphical Encoding for Information Visualization: Using
  Icon Color, Shape, and Size to Convey Nominal and Quantitative Data</b></i>.
  PhD thesis, Virginia Polytechnic Institute and State University,
  Blacksburg, Virginia, November 1997.
  <A HREF="http://vis.cs.brown.edu/docs/pdf/bib/g/Nowell-1997-GEI.pdf.html">(pdf)</A>
  <A HREF="http://vis.cs.brown.edu/results/bibtex/Nowell-1997-GEI.bib">(bibtex:
  Nowell-1997-GEI)</A>.<br />