A city, no matter how efficiently planned out or how beautiful, is rendered worthless without people.  It cannot exist because it takes people to make a city.  It is people who will take the empty shells of buildings and make them function.  It is people who take space and turn it into places.  It is people who anchor the city in time, even if only for a fleeting moment.  If we examine de Certeau"s three requirements for the ideal or "concept" city, we find that it leaves us with a city without life or presence.  "Rational organization must repress all the physical, mental and political pollutions that would compromise it" -- we imagine that this must be brought by the inhabitants of the city, not by the urban structure itself.  "The substitution of a nowhen, or of a synchronic system, for the indeterminable and stubborn resistances offered by traditions" -- it is the people who must establish and break the traditions of the city, it is not for the city to make its own history.  "The creation of a universal and anonymous subject which is the city itself" -- the city is to bring nothing but the basis of stimuli to the population and it is the people who are responsible for making it come alive and giving it meaning.  Moreover, it is people who order city space, making it real for themselves.  In effect, the city provides pen, ink and paper and it is the people -- namely the pedestrians -- who provide the story. 
 

According to de Certeau, it is specifically the walking people who bring the city to life.  They do not have that god-like "all-seeing power" and are therefore trapped within the "city"s grasp." They are at ground level and looking down, and ironically it is these people who write the "urban text" without being able to read it.  More importantly to note, it is the mass movement of people who write the text.  With thousands of individuals each writing his own story and giving his own interpretation, the city is pieced together something like a patchwork quilt of individual viewpoints and opinions.  "The created order is everywhere punched and torn open by ellipses, drifts, and leaks of meaning: it is a sieve-order." It takes a single city to provide the stimulus, but it requires a multitude of people -- all unaware of their role in the creation of the city -- to provide the meaning.  

The space once defined, only remains thus defined for as long as the individual defining the space remains there.  The definitions are fleeting, one replaced by the next as a second pedestrian assumes the position of the first.  De Certeau defines the verb "to walk" as an action of "lack[ing] a place": this should serve to illustrate just how the stories defining space disperse and disintegrate as the pedestrian moves out of a place, for the definition of city space is similar to walking itself.  It holds to no single space, and it is in no way anchored.  The stories and legends allow people to move freely within city space, but without them there can be no space to move within at all, for space ceases to exist.  Thus it can be seen that as the subject moves through city space, so he defines it: there is no city space without him.  He creates the space to move through as he moves through it.  The city is subject to the views and stories that the mass population project upon it.  The city is there to be manipulated, molded and used, and yet it emerges the same at the end, for no image projected upon it can ever remain since the pedestrians are not static and nor is the space in which they move.  Indeed, I would go as far as to say that the space is not even real, but simply make-believe.  

All quotations from de Certeau taken from Walking in the City,  
The Practice of Everyday Life, 1984