## What

Show a table or list of items as a circle instead of a column. Draw connections among items through the interior of the circle.

## Use when

You have a long list or table of items and you need to show arbitrary relationships among them: flows, connections, affinities, similarities, and even numerical values (encoded by the thickness of the connection).

## Why

A circular presentation enables free-form connection lines to be visualized far more easily than a line or column of elements would permit. Such connections have a shorter, straighter distance to travel when drawn between points on an arc than points on a line, and viewers can usually see patterns in the data more easily. (This is not always the case. If you can, try out different types of connection visualizations to see if it’s true for your particular data sets.)

Even when there are no connections to draw, some kinds of tabular data might be easier to see when drawn as a circle—very long data sets with both large-scale and small-scale features, for instance. Large-scale features might include groups and clusters, upper levels of a hierarchy, or labels for large numbers of items. See the examples for illustrations.

From the website of Circos, a creator of radial table designs, comes this explanation:

“Within the circle, the resolution varies linearly, increasing with radial position. This makes the center of the circle ideal for compactly displaying summary statistics or indicating points of interest (i.e. low resolution data) which the reader can then follow outward to explore the data in greater detail (i.e. high resolution data).”

Finally, radial information graphics can be beautiful. When drawn skillfully, these kinds of visualizations are fresh, attractive, and engaging.

## How

Bend the linear table or list into a circle and put the text labels around the outside of the circle (if you need them). Some Radial Tables place the x-axis on one half of the circle and the y-axis on the other half; this is useful if your data table is trying to show connections between two one-dimensional sets of items.

If the original table shows multiple columns of dependent data—numbers, bars, pictograms, scatter plots, and so on—arrange those either inside or outside the circle, depending on the visual scale and interrelatedness of these features. Large-scale, convergent features should go inside; small-scale, detailed, divergent features should go outside, where they have more space.

If the items in the table are categorized, you could encode those categories as groups separated by gaps, or in different colors, or as arcs parallel to the circle (either inside or outside the data axis).

Inside the circle, draw relationships among the items. Those relationships might take the shape of free-form lines or arcs between table cells. The line color and thickness can encode additional variables about the relationships, such as source or destination (color), and volume or strength (thickness). Sometimes these relationships need to be drawn so thickly that they’re hard to distinguish from each other. Here are some ways to deal with that problem:

• Eliminate superfluous lines; draw only what you want viewers to focus on.
• Use drawing algorithms that can cluster lines together and keep them visually organized.
• If the graphic is interactive, use techniques such as Data Spotlight and Dynamic Queries to let the user see chosen subsets of the lines.

You may need to explain how to interpret a Radial Table. These graphics can be very useful to the patient and informed viewer, but their meaning may not be immediately apparent to a viewer who is naive or not motivated to spend time studying the graphic carefully. If your users are likely to move on without understanding the Radial Table, consider simplifying it or using an easier alternative rendering.

## Examples

SolidSX Software Explorer is an application that draws Radial Tables of software packages. It shows dependencies, calls, and hierarchical relationships among code elements in a library. Note the containing arcs around the outside of the circle (showing the static hierarchy), and the call-graph lines within the circle, which are carefully drawn for clarity.

From the Eigenfactor Project and Moritz Stefaner comes an elegant diagram of citation patterns among branches of science. There are many connections, but they are drawn so well that the viewer can follow them with some degree of success. The diagram shows which fields of science are more insular than others (e.g., economics) and which are better connected.

This genetics diagram demonstrates that the curved format can be effective in illustrating data patterns other than connections. The diagram could have been “unrolled” into a horizontal strip-chart format, but this version is more compact and arguably more readable than a long, thin linear chart. Note that the line charts on the inside of the table are a larger-scale feature than the tiny multicolored slivers around the outside of the circle, so they are appropriately shown inside the circle.

## In other libraries

Relation Circle at Interface Design Patterns

For many more examples, visit the Circos and Visual Complexity websites.