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Interactive Fan Charts: A Space-saving Technique for Genealogical Graph Exploration

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Interactive Fan Charts:A Space-saving Technique forGenealogical Graph ExplorationGeoffrey M. Draper and Richard F. RiesenfeldSchool of Computing, University of UtahAbstractFan charts are a popular method for displaying family trees in a compactway. We extend the concept of fan charts to include a number ofinteractive metaphors, thus transforming what was a static display mediuminto an interactive tool for browsing and editing genealogical data.Keywords: genealogy, information visualization, radial space-filling layouts1. IntroductionA fan chart is a radial space-filling technique for displaying genealogical graphs. In afan chart, a person’s name is drawn in the center of the graphic, surrounded by concentricrings containing the names of the person’s ancestors.1 Most commercial family tree-generating software packages, including Family Tree Maker [2] and PAF Companion [5]support the creation of fan charts. More recently, open source projects such asPhpGedView [1, 4] also support fan charts. Fan charts are a popular method forvisualizing family trees, due perhaps in part to their aesthetic appeal as well as theircompact appearance relative to the more common tree-based pedigree chart (Figure 1). Figure 1. (left) A fan chart. (right) A standard pedigree chart.Although pedigree charts are easy to understand, they do not necessarily make optimaluse of the available space. Indeed, much recent research has been devoted to findingbetter layout algorithms for pedigree charts [3, 6]. A natural argument in favor of fan1 Fan charts exist in a number of sizes; the most common variants are quarter-circle, half-circle, and full-circle. To simplify the present discussion, we focus exclusively on full-circle fan charts in this paper,recognizing that the techniques introduced herein are applicable to fan charts of any size.page 1 of 7charts over ordinary pedigree charts is that the circumference increases with eachsuccessive generation, thus, as the number of nodes grows, so does the available space inwhich to render them. This quality of fan charts is immediately appealing, butunfortunately it does not grow fast enough. Recall that the number of ancestors in thechart grows exponentially, doubling with each generation. Assuming each ring has thesame width, we see after a little analysis that the area of the chart only grows linearly witheach generation. Some more elaborate schemes, like the ones shown in this paper, giveincreasing width to each successive outer ring; each ring width is increased by an additiveconstant. This defers the space crisis somewhat by introducing a (slow) quadratic growthrate for the area of each new ring. However, we are still faced with fundamentallymismatched growth rates. Relatively quickly, the slow polynomial area growth will beinundated by the exponential growth in the number of ancestor nodes. Therefore spaceremains a scarce commodity even in moderately-sized charts, despite the ever-increasingcircumference.To address this concern, we propose the interactive fan chart: a radial graph in whichnodes can be selectively expanded or collapsed so that a greater proportion of theavailable space is dynamically allocated to nodes of current interest. In addition, weintroduce a number of interactive techniques that transform fan charts from a staticdisplay medium into a tool for real-time data browsing and exploration.2. Interactive TechniquesWe present a detailed discussion of each of our proposed techniques below.2.1 Expand and CollapseAt each concentric level of a static fan chart, each ancestor is normally allotted the sameproportionate space. However, for interactive browsing, this is likely not optimal, for auser may wish to commit more resources to one particular branch as he or she explores agiven line of the family.We propose a method for selectively reassigning space from nodes of lesser interest toimprove the readability of the line of focus. In an interactive fan chart, the user cancollapse a node by selecting it with a mouse or other pointing device. The selected nodeand all of its ancestors diminish in size, while the adjacent nodes grow to absorb thevacancy. (An alternate scheme would be to select the node that one wishes to expand,rather than the node to be collapsed. In our implementation, this behavior can be toggledvia a menu option.) The enlarged node is rendered with a thick border as a visualreminder that it has been expanded (Figure 2). Selecting the expanded node reverts thediagram to its previous size. The transitions of expanding and collapsing nodes aresmoothly animated so that the user’s sense of context is preserved [7].The ability to expand and collapse nodes in a fan chart is especially useful in the situationwhere one branch of the family tree has been more thoroughly researched than another.In a static fan chart, space is allocated for all ancestors regardless of whether their namesare known. This results in large blank areas in the chart, meaning less available space forpage 2 of 7regions of the chart that are more dense with information. By allowing the user totemporarily hide such sparsely populated regions of the chart, interactive fan chartsprovide opportunities for inspecting the denser regions of the graph in more detail. Figure 2. (left) Original view. (center) Selecting a node causes it to collapse, while itsadjacent node expands. (right) Selecting the expanded node restores the nodes to theiroriginal sizes.2.2 Selecting a New Root NodeIn a static fan chart, the root node is rigidly assigned at the time the chart is created andcannot be modified. However, some systems now relax this constraint by allowing newroots to be chosen dynamically [4]. Our interactive fan charts likewise allow the user toselect a new root for the chart, be it a child of the current root node or an arbitrary nodefrom the database. The following two subsections describe how this is done.2.2.1 Selecting a Child of Current Root NodeIf the current root node has at least one child, a small circle is drawn in the center of thechart. Selecting this circle with the pointing device gestures that a child of the currentroot node should be the new root node. If the root node


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