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Parallel Line Graphs

1 June 2010
Sagit Salmon

Parallel Line Graphs (Parallel Coordinates) is a method for graphically presenting multiple data points on a single chart. The chart displays several graphs in parallel, each reflecting data related to various dimensions.

This method was first invented in the 19th century by Maurice d'Ocagne but was "reinvented" in 1970 by Alfred Inselberg to present data in a multidimensional format.

The method was developed during the 1970s, and today, it is mainly prevalent in academia and the scientific world but less so in business companies and customer service organizations.

This is not surprising, as charts presented using the parallel coordinates method appear complex and crowded, and the placement of data on the graph is not simple.

However, the advantages of a chart presented in this method, beyond the ability to display data in a multidimensional format, are that it reflects a broad picture and helps analyze an existing situation. Additionally, the chart is interactive, allowing for highlighting or illuminating selected data (by color, for example...) while comparing them to others.

The parallel coordinates method is your data story.

In the example below, a chart of a group of baseball players is shown.

  • The chart compares the team's players according to several parameters.

  • Each graph represents one player on the team.

  • All parameters and numbers are on the graph, complementing each other to form a complete picture.

  • The colored graphs represent two players chosen for display, and the gray graphs reflect the rest of the team members (not selected), so the comparison is against all players in the team.

  • The chart is interactive, so the two players displayed in color can be changed anytime.

Parallel  Line Graph

So what did we have?

The parallel coordinates method presents multiple data points in several dimensions on a chart.

The method's advantages are also its disadvantages: We gain a broad picture and in-depth analysis of the data, with the ability to highlight selected data (interactivity), but in return, we may encounter complexity in data input and difficulty understanding the chart by the reader.

Source: Better Know a Visualization: Parallel Coordinates, Zach G., April 2010

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