A Galaxy Chart is designed to show data that originated in a hierarchical, element structure. Most commonly, the Galaxy Chart is used to display, with accuracy, data housed within a Work Breakdown Structure (WBS) within a single figure. It illustrates not only proportions and magnitudes but also relationships between elements. Any data that has several levels or groupings can be shown using a Galaxy Chart. Each element is represented by its own circle and all relationships between circles are illustrated using straight lines. All circles are sized proportionately by area and are arranged in a decreasing, clockwise manner.[1]
Galaxy Charts differentiate themselves from other chart types, such as Pie Charts, by showing several levels of the data in a single chart and by displaying all element-to-element relationships. In addition, Galaxy Charts have an arrangement that is easily repeatable and has visual cues to help the viewer see how the data are arranged.[1]
Example
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The following example chart is based on the FY10 United States Federal Budget grouped by category[2]. The functions, sub-functions, and dollar amounts are taken directly from the source.
The top-level, i.e., the Federal Budget, is equated to the Sun, and each of its children to Planets. On the chart, each cost element of the Federal Budget has its own circle. The Sun is in the middle and its children, i.e., the Planets, “orbit” the Sun. Lines drawn between them illustrate this relationship. The children’s children, i.e., the Moons, are in orbit around their respective parents, i.e., the Planets. The entire hierarchy uses this parent-child orbiting tactic.[1]
Throughout the hierarchical structure, each circle’s area equals its cost, and, at every level, the parent-level area equals the sum of the areas of its children. This sizing technique means that top-level, larger cost elements are large circles and the low-level, smaller cost elements are small circles. In many cases, some circles become so small that they are almost unnoticeable. This is done by design. Galaxy Charts help one to focus on larger, more significant cost elements and to de-emphasize smaller, inconsequential cost elements.[1]
In a Galaxy Chart, the parent’s child elements circle the parent in a clockwise manner, at an ever-decreasing distance. For the total circle, i.e., the Sun, the largest element is located immediately below. For all other circles, the largest circle begins 180 degrees from where the parent line connects. In both cases, the remaining elements are evenly spaced around their parent circle in a decreasing order relative to their size. The distance between the parent and child also decreases clockwise around the parent circle. The combination of decreasing circle size and decreasing circle distance creates a Pareto-like effect, making it very clear to the viewer how the circles are ordered.[1]
All circles contain an element label and a dollar amount. The element label represents the name of the element, and the dollar amount is the value represented by the circle. If the element has children, it contains percentages inside the circle, and these percentages relate to their respective children. At the beginning of the line connecting a parent to its child, a percentage displays that child’s percentage of the total cost, i.e., the Sun’s cost. The percentage text is relatively small, when compared to the main circle text, and is gray in color so as not to detract visually from the rest of the text. In the smaller circles, the text is often unreadable when printed. Nonetheless, text is provided to allow zooming-in.[1]
This Federal Budget Galaxy Chart contains 106 cost elements on a single graphic, with all relationships clearly illustrated. Many other standard chart types can only show a fraction of this number.
Development
editThe Galaxy Chart concept was originally developed by Technomics, Inc. and first presented at the 2012 SCEA/ISPA Conference in June 2012 where it won Best Overall Conference Paper [3]. The software to generate a Galaxy Chart is patent pending, but will be available soon for free at www.galaxycharts.com. Galaxy Charts are not a default chart type in any other software package.[1] Future research and enhancement is being conducted by Technomics, Inc. and current uses of the Galaxy Chart include program management, cost estimates, Earned Value Management (EVM) and a myriad of other applications with data sets in a hierarchical structure.