What are the challenges faced by big cities?

The cities face many problems, the main one being environmental problems.
City development causes great harm to the ecology and the surrounding environment. Natural features, like hills were flattened out to create more space in the cities. Due to the vast population, air, water and land get polluted.
Another major challenge faced by big cities all over the world was noise pollution. The heavy traffic and the blaring horns are the cause of this noise pollution.
Smoke from factories darkened the city skies and caused health hazards for the city dwellers.
Factory wastes contaminated waterways and land.
The need for housing destroys the greenery and results in poor quality of air.
Governments all over the world are doing their best to control pollution and provide a safe living space for the growing city dwellers.