Treemaps are a growing trend in online data visualization and you’ve likely spotted one or two around the web. But what are they?
Treemaps, sometimes written as “tree maps,” display hierarchical information in a series of clustered rectangles, which together represent a whole. The size of each box represents a quantity. Treemaps also can use color to represent any number of values, but it is often used to categorize the various boxes within the treemap.
Interactive and news designers are taking advantage of treemaps to represent a variety of information as in the examples below.
To start you off, here is a simple treemap created by BBC News to visualize what types of web sites are most popular on the web. The “Search/Portal” block takes up the largest space because those sites are most popular. You can also hover over each block to see which sites within the categories are popular. For example, eBay and Amazon are the largest blocks in the larger “Retail” block because they are two of the most popular retail sites on the web.
To visualize something as large and complex as the budget of the United States of America, the Times turned to a color-coded and easy-to-navigate treemap. The treemap is divided into sections, including national defense and social security, and the budgets within those divisions are represented by smaller blocks. You can hover over the smaller blocks to see the monetary amounts and read further descriptions. The colors of each block represent how much each allotment has changed since last year — red represents a decrease and green represents an increase.
One of the most common ways designers are using treemaps is to track the social media response to a particular event. CNN uses a treemap to visualize the discussion of the World Cup among Twitter users. Instead of a single color, the blocks in the CNN treemap are represented by the flag of the country that is being discussed. In the example below, Argentina occupies the largest, leftmost block because it was, at the time, the most discussed World Cup team.
NBC created a similar “Tweet Tracker” to visualize the discussion around the 2010 Winter Olympics. MTV and Stamen Design used interactive treemaps to visualize the MTV Movie Awards and Video Music Awards (VMAs).
Nike’s Twitter treemap, also created by visualization powerhouse Stamen Design, uses proportionate blocks to represent which NBA teams are most discussed on the social network. The Los Angeles Lakers, 2010 NBA champs, are the most discussed team and therefore occupy the largest block.
Finally, an oldie but goodie — you can’t talk about treemaps with mentioning the Newsmap, an interactive treemap that categorizes the news aggregated by Google News. The various colors represent different sections such as business or politics. The older a news story is, the darker the box becomes. The size of the boxes represents how many similar stories also appear in Google News.
You can produce a tree map a number of ways, including using Illustrator or Photoshop to draw proportionate rectangles or by using the visualization tool Many Eyes. You can also use advanced tools like Google’s Visualization API.
In order for treemaps to be easily understood by the viewer, they must be clearly labeled and, for the most part, uncluttered. A treemap can contain any number of boxes, but space restrictions limit how many boxes can be included without it looking like a big mess.
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