There is a big issue that has not been answered properly by urban planners, architects, engineers, geographers and other people who study cities. The issue is the one related to the city limits. Obviously, it is difficult to define it and more difficult to do it in a few blog posts, but I want to make an approach to some matters that are important in this question in the following three posts.
We are witnessing a huge urbanization and an accelerated process in city growing. But, apart from the urbanization process question, there is a more interesting question for which I do not have an answer, and it is How big can a city be? I have not found a definition of city containing the size component yet.
Despite this I already know that cities somehow are defined by people gathered, so maybe we can have some answers thinking about that matter. Going through this path we can think that people also need some “stuff” for living. Firstly, I am sure that people need to feed themselves, but nowadays food production happens outside the city, so this will not be the key factor to define our cities limit, although it was before the 15th century. Secondly we can think about energy, but we can reach the same formerly conclusion, energy can be produced in a “national” scenario, so it cannot be the defining question. We can also think about a great number of issues and we usually reach the same conclusion, we can think about information, goods, money, etc. and we have to assume that this ´stuff´ can come from out of the city limits.
To solve this problem I started to think more in people´s relations and in the advantage of proximity relations between people and I found one service that has to be given in the city to take advantage of agglomeration, transportation. Transport has to solve the physical problem of communication inside the city and it has to solve the problem in a certain time. It is assumed that a person can´t spend longer than a certain time to go and return to or from his house (one hour/one hour and a half maximum per trip). So with the fastest transport modes that we nowadays have, cars and metropolitan railways, we could imagine a city limit defined by their influential area and by the time that a person can spend in transport in a single day.
I think that this is an interesting point of view, because we can see cities as relational systems more than agglomeration places and this vision allows to link people with the city limit through the physical needs of communication.