In the case of the Philippines, the National Capital Region (i.e., NCR, comprised of Manila and its environs) has grown into a megacity of close to 20 million people. Such a population is sustained by inputs of food, energy, water drawn from outside the NCR itself, resulting in an environmental footprint that far exceeds the land area of this major urban center. A similar pattern also occurs for many large cities elsewhere in the world. There are a number of other cities like Metro Cebu and Metro Davao which are facing similar problems. With PSE, a mathematical model can be created of the entire metropolis so that various policy scenarios can be simulated such that there is an optimal benefit for the population.