Treemaps Bloom

July 2, 2001 (Computerworld)

A second spring is blooming for a uniquely visual interface that lets users view thousands of files at once as proportionately sized rectangles, grouped to represent folders.
These "treemaps" will see increasing use in applications that can give users a fast yet comprehensive understanding of complex structures, developers say.
Treemap developers from across the U.S. and Europe met at the University of Maryland, College Park, in June to share research results.
New algorithms offer improvements. They maintain ordering, such as by size, alphabet or date created; reduce surprising movements of file images as sizes change; and prevent having a screen with hundreds of razor-thin slices and a handful of squares.
New "squarification" algorithms ensure that all files will be represented as squares. One application adds color and 3-D shading techniques.
An open-source Java treemap library, a work in progress, is downloadable for free.
"We were thrilled to see how people have started with our basic idea and taken it past where we dreamed it might go," says Ben Shneiderman, a University of Maryland professor who 11 years ago built the first treemap (www.cs.umd.edu/hcil/treemaps/treemap2001).
The first treemaps used a simple slice-and-dice algorithm that sometimes produced arbitrary and extreme shapes. The newer squarification algorithms assign space based on the weight of the attribute selected - such as size or most recent date of alteration - and arrange the resulting file images to give a more square look to each group.
Hip to Be Squarified
New York-based SmartMoney.com has incorporated a squarified treemap view in its MapStation application at www.smartmoney.com/ mapstation. Stocks are represented by colored rectangles, and traders can make size and color represent any of several dozen financial indicators. For example, size can represent a stock's price at the moment, while color can indicate whether a stock's performance that day is hot.
In ordered treemap applications like SmartMoney's, users can select a "pivot point" based on a file attribute such as median size. All file images will be sized in relation to the pivot file's designated size. Views that use this kind of pivot point tend to offer smoother update views, an important consideration when the treemap must present the results of dynamic queries, such as in a photo-browsing application.
In developing his PhotoMesa photo browser, Ben Bederson, director of the Human Computer Interaction Laboratory at the University of Maryland, faced a visualization problem new to treemaps. A photo file size may vary, depending on resolution, but all photos must be represented at equal size, although their orientation may be landscape or portrait. He developed a new algorithm, which he calls a "quantum treemap," that extends the ordered treemap to present groupings of photos in continuous rows.
One researcher with a unique vision is Jack van Wijk, a professor at Eindhoven University of Technology in the Netherlands. The more complex the hierarchical structures, the more difficult the tree is to visualize, he says. "I asked myself, How can we emphasize structure?" van Wijk says.
His answer was to apply 3-D computer graphics techniques to treemaps to develop his "trees and cushions" treemap application, SequoiaView.
File images created by SequoiaView (www.win.tue.nl/sequoiaview), a free disk-browsing tool, can make large files or files that haven't been accessed in a year immediately evident. Shading creates a 3-D cushion effect, differentiating each rectangle representing a file from adjacent files. Color coding each file further differentiates one from another.
Christophe Bouthier, a graduate student at the Lorraine Laboratory for Research Into Information Technology and Its Applications (LORIA) in Nancy, France, maintains a free Java library at http://sourceforge.net/projects/treemap for implementing Shneiderman's Treemap 2000.
Treemap research is still growing. Van Wijk is developing a botanical treemap in which hard drives are represented as 3-D espaliered trees, directories and subdirectories as main branches and twigs, and files as leaves. Mohammad Ghoniem and Jean-Daniel Fekete at the Ecole des Mines de Nantes in France are working on animating the updating of a hierarchical view.
Treemaps are showing up in a variety of applications. At Stanford University, doctoral candidate Peter Demian is using the LORIA library to create treemaps for a building design knowledge visualization and reuse application. And at the Burlington Northern Santa Fe Railway in Fort Worth, Texas, treemap views help managers track equipment and personnel at a glance.
Look for more applications to start sprouting treemap views, Shneiderman says. For starters, he says, the University of Maryland has licensed 50,000 copies of its treemap application to Micro Logic Corp. in Midland Park, N.J., for use in the company's DiskMapper software.