As part of his larger mission of promoting "fact-based" public health policy, Swedish physician Hans Rosling founded Gapminder.org, which aims to make world health data available and understandable to everyone. Back in 2006, Rosling gave a well-received TED presentation on the principles of Gapminder, showing, among other things, relative historical changes in life expectancy and GDP. (He spoke again in 2007.)
Rosling acknowledges that there are some small flaws and inconsistencies with data derived from all these different sources, but believes that the comparative results are far more significant. Check out the vast difference between Mauritius and Congo in income per person and life expectancy (shown on the Gapminder site and in the '06 presentation); consequently, says Rosling, using the term "sub-Saharan Africa" to describe both of these countries is vague to the point of uselessness.
His point: The more easily data and details can be visualized and compared, the more effective policymakers can be in formulating and targeting international aid.
The software Rosling uses to make his visualizations (formerly known as Trendalyzer) is now available as an Official Google Gadget called Motion Chart.