Problems
Over population is an increasing issue in most mega-cities, for example Mexico City grew from one million to over 15 million in only 50 years. This is a problem because a higher population has a higher demand for more housing and services. A high population can have health risks due to the ease to spread a disease. Other issues are traffic jams and poor air quality
Comparing Mega cities
Population
The largest mega-cities are Tokyo,Karachi, Delhi, Seoul, Shanghai, Mumbai, Mexico City, São Paulo, Beijing, Osaka, New York and Jakarta. In that order.