Why it looks like this

In Aztec times Iztapalapa was a lakeshore town famous for its chinampa gardens, at the foot of the Cerro de la Estrella where the sacred New Fire ceremony was held. The lake was drained over the centuries, and in the 20th century the flat lakebed filled with streets.

Most of that growth was self-built: families laid out their own blocks faster than the city could plan them, producing today's vast, tight grid holding roughly 1.8 million people — with the volcanic hill still rising green in the middle of it.