Do cities widen the gap between rich and poor?
Several explanations for increasing income inequality have been proposed, including skill-biased technological change brought about by computers and modern telecommunications, the expansion of global goods and labour markets, and changes in countries’ skill and age distributions. Yet one pattern has gone largely unnoticed: inequality is especially strong in large cities. At least one-quarter of the increase in earnings inequality in the US during 1979-2007 is explained by the high growth of earnings inequality in large urban areas (Baum-Snow and Pavan 2013).
Reading Development 
I was wondering if you had any thoughts on the optimum number (or range) of people living in a city in order for sustainability, good incomes and a safe environment?