Energy intensity measures, defined as the ratio of energy use to gross domestic product of a country, are widely used to study the productivity of energy use in an economy. Unlike conventional primary and/or final energy intensities, useful work intensity (useful work/gross domestic product)...

According to a study by the United Nations on urbanization, the world population living in cities has been increasing exponentially and will continue to do so in the next years. From 1950 to 2007 the percentage of urban population has increased from 29% to nearly 50% and the projections made...