Mexico City is such a big city that most inhabitants would have problems defining its boundaries. Most people could probably name 2 or 3 access routes, but defining its boundaries is an exercise better left to city planners. A couple of months ago, I had the opportunity to transit through a new highway connecting the East of the city with a point far to the North. This highway is so new that in most cases the view was occupied by farmed land on one side and a clear urbanized area on the other. For those who have been to Mexico City you’ll appreciate how strange this is, as the city always seems endless in all directions. In the map below, this highway is marked in red.
The further North this highway goes, the less urbanized the region is, until it connects with the main highway heading to the North. Of course, the advance of urbanization is such that it will only be matter of time before the city has surpassed this new limits. In the same map I’ve indicated in blue what is known as “Anillo Periférico” and in green the “Circuito Interior”, both high-speed avenues that were built at the edge of the once smaller city. Infrastructure has a way of attracting dwellers and making it possible to sustain edge neighborhoods.
Defining city boundaries can’t be done based on administrative divisions. Mexico City, for example spans two different states and there is absolutely no indication on the ground that you’re crossing any division. Real boundaries are probably better defined by what is practical and possible with the given infrastructure of the city. That is, if a person can make a daily commute (as hard as it is) using public transport or infrastructure, it is likely the economic output of that person contributes to the overall output of the city. Therefore the practical boundaries of a city should be defined by the availability of infrastructure nearby (subways, trains, highways).
One can only imagine what effects will better transportation systems have on urban sprawl. Are the gigantic sprawling areas often referenced by science fiction authors a necessary consequence of better and faster vehicles? Or is there a way to promote really long commutes that would effectively allow people to participate in the economy of a city without living anywhere near. Trains reaching 400 km/h are a reality and a commute of half hour could effectively take you far enough.
One thing is certain, Mexico City planners don’t share this vision as they are already delimiting the new boundaries of the city and it would seem they just picked an area where there are plenty of opportunities to urbanize. I have no doubts that people will follow. Too bad.