History of Heatmap technology

An extract from 'A History of Treemap Research at the University of Maryland' by Ben Shneiderman

During 1990, in response to the common problem of a filled hard disk, I became obsessed with the idea of producing a compact visualization of directory tree structures. Since the 80 Megabyte hard disk in the HCIL was shared by 14 users it was difficult to determine how and where space was used. Finding large files that could be deleted, or even determining which users consumed the largest shares of disk space were difficult tasks.

Tree structured node-link diagrams grew too large to be useful, so I explored ways to show a tree in a space-constrained layout. I rejected strategies that left blank spaces or those that dealt with only fixed levels or fixed branching factors. Showing file size by area coding seemed appealing, but various rectangular, triangular, and circular strategies all had problems. Then while puzzling about this in the faculty lounge, I had the Aha! experience of splitting the screen into rectangles in alternating horizontal and vertical directions as you traverse down the levels. This recursive algorithm seemed attractive, but it took me a few days to convince myself that it would always work and to write a six line algorithm. This algorithm and the initial designs led to the first Technical Report (HCIL TR 91-03) in March 1991 which was published in the ACM Transactions on Graphics in January 1992. Choosing the right name took probably as long, but the term 'treemap' described the notion of turning a tree into a planar space-filling map. (NB.Incito use the term 'heatmap' in place of 'treemap')

My initial design simply nested the rectangles, but a more comprehensible design used a border to show the nesting. Finding an effective visualization strategy took only a few months but producing a working piece of software took over a year. Brian Johnson implemented the algorithms and refined the presentation strategies while preserving rapid performance even with 5,000 node hierarchies. The TreeViz application ran on color Macintosh models and led to the widely cited paper (HCIL TR 91-06) jointly authored paper in the October 1991 IEEE Conference on Visualization. This paper was reprinted in Readings in Information Visualization. I think treemaps are a convenient representation that has unmatched utility for certain tasks. The capacity to see tens of thousands of nodes in a fixed space and find large areas or duplicate directories is very powerful.

Various developments took place in the intervening years and one of note was that of Alexander Jungmeister who worked with Dave Turo's implementation and built a stock portfolio visualization that showed clients, portfolios, industry groups, stocks and trades (HCIL TR 92-14). Size might indicate worth of the holdings and color might indicate the degree of increase/decrease in value. I still believe that a worthwhile application would be a stock market monitor that would show the current daily trade activity. It could present the 30 Dow Jones Industrials, the Standard and Poor's 500, or all 2700 companies on the New York Stock Exchange. They would be grouped by industry (airlines, chemicals, drugs,...), area coded by volume of trading, and color coded by increase/decrease. Click here for further detail.