By and large, people have the wrong idea about Mexico City. To many the name alone summons two words: crime and pollution. No doubt there are areas to be avoided, but the Distrito Federal is packed to the gills with decent people who will usually look out for one another, and for you.
Pollution summons visions of unwalkable, megahighway-filled cities jammed with cars, which this is not. The smog is real: the Aztecs built their city of Tenochtitlan in a high (7,347 feet) valley that often waits days for the air to move. But there are more than 6 million cars in the city, fewer than three for every 10 of 22-million-something inhabitants (reports vary). Truth is, those living in the capital do so more sustainably than most people in the industrialized world, at high—yet comfortable—densities (though not in high-rises), and move mostly on foot and by public transit. (If you are tempted to drive this Gordian knot of merged villages, well, we would recommend that you not.)
Most of Mexico City is aligned on two major intersecting thoroughfares: Paseo de la Reforma and Avenida Insurgentes—at 34 km (21 mi), the longest avenue in the city. Administratively, Mexico City is divided into 16 delegaciones (districts) and about 400 colonias (neighborhoods), many with street names fitting a given theme, such as rivers, philosophers, or revolutionary heroes. The same street can change names as it goes through different colonias. So most street addresses include their colonia (abbreviated as Col.) Unless you're going to a landmark, it's important to tell your taxi driver the name of the colonia and, whenever possible, the cross street.