No, it’s not the obesity epidemic spreading to typography, but rather a novel way of using numbers to visually convey information. A new approach to typesetting numerals, FatFonts, varies the stroke of each digit so that its area is proportional to its value. That is, the digit “2” is double the area of “1,” the digit “3” is triple the area of “1,” and so on. It seems easy at first, but you can see where things would get tricky. Via New Scientist:

The team measured the area of each number and then thickened or thinned sections of it so that the total area scaled in proportion to each number's value. A digit like 2 did not need much thickening as it already covers a larger area than 1. By contrast 7 needed a lot of thickening as its total area is small relative to its value.

And then:

To represent numbers with multiple digits, the team devised a system of nested digits. In the case of 489, the 8 sits inside the 4 and covers an area 10 times smaller, while the 9 sits inside the 8 and covers an area 10 times smaller still. This makes 999 the largest number possible with FatFonts, as the smallest part of a four digit number would be too little to see easily.

What applications are there for this?

To demonstrate the usefulness of the concept, Nacenta’s team used FatFonts to create a map of Sicily in which each number represents the height of the ground at that geographical location.... For easy reading they scaled the heights so that the largest is represented by the number 99. As with existing heat maps, where areas associated with larger numbers appear proportionally darker, standing back from the map makes it easy to identify mountainous regions. However, the FatFonts map has the added advantage that moving closer lets you compare points numerically, too. FatFonts are most effective when printed on large, high-resolution wall displays, says Nacenta. These are big enough to see the individual numbers, as well as larger-scale trends.

It would be interesting to pit the FatFonts against the so-called Ecofont, the latter of which purports to save ink and toner by printing glyphs with holes in them.