I cannot claim to know what makes a vibrant city, but over the course of my travels, I visited cities of different means, some certainly more successful than others. The poorest cities I visited seem to represent less diverse ecosystems, and by that, I mean they exhibited less stratification in wealth, transportation, and housing options. In these, the majority of the populations were very poor, whereas a middle class was almost nonexistent. The wealthy were extremely so, especially by the standards of the rest of the country. There were clear distinctions between classes, and in turn, very few classes.
This was evident in São Paulo, Rio de Janeiro, Cairo, Mumbai, and Dhaka. On the other hand, cities such as Hong Kong, Seoul, Tokyo, and New York seemed to represent far more complex ecosystems, with wider variations in wealth, transportation, and housing options. In the latter (more complex), high population densities played a role in creating vibrant cities, versus the former (simpler), where high population densities were the effect of increasing poverty levels.
Over the course of my travels, I met many people who were striving to change their lives for the better, when often times it seemed their challenges were insurmountable. But they simply didn’t see it that way. In some of the worst living conditions I had seen on the trip, I found communities of people that remained hopeful because their conditions were constantly improving. This sort of optimism was hard for me to understand before I visited these places, but it remains something I will be hard-pressed to forget.