Daniel A. Keim Ming C. Hao Umeshwar Dayal Meichun Hsu Pixel bar charts: a visualization technique for very large multi-attribute data sets? 20-34 2002 1 Information Visualization 1 http://dx.doi.org/10.1057/palgrave/ivs/9500003 db/journals/ivs/ivs1.html#KeimHDH02