The cities with the highest density of millionaires has been revealed, for the first time ever, by the wealth consultancy group Spear's, with analytical help provided by WealthInsight. Even among the ultra-wealthy, there exists great income inequality. In the top three cities, for example, you could scarcely throw a gold ingot without hitting a million- or billionaire; that trifecta is home to a full three-quarters of the world's high net worth individuals. (For this study, a millionaire is defined as anyone possessed of more than US$1 million in net assets, exclusive of primary residence.) So, whither the richest of the rich? Read on.