The map shows the Gini Index (in %) of income worldwide, according to latest published data by World Bank in July 2014 (individual data points may be more than 10 years old).
Data Source: Table "Distribution of income or consumption" in tables World Development Indicators The World Bank (2014)
Gini index is a measure of income inequality. A nation where every individual's income is equal would have a gini index of 0. A nation where one individual gets all income, while everyone else gets nothing would have a gini index of 100. Higher gini index for a nation means more income difference between its people.
The average of Gini index scores in this map is about 40. All countries color coded in green have gini index scores less than 40, while those in shades of red have gini index above 40.

This is a derivative work on BlankMap-World6.svg available on wikimedia commons. It has been tested with W3C.
Own work
M Tracy Hunter