"Of Other Spaces" (Des espaces autres), also commonly known as "Heterotopia", was initially a lecture carried by Michel Foucault to a group of architects in 1967.
In "Of Other Places" Foucault starts by looking at the historical development of western space perception, starting from what he terms "espace de localization" in the middle ages, through the "etendue" (extending) form the time of Galileo to the modern "emplacement". Emplacement means, according to Foucault, that relations between locations in space are the constitutive principle of space perception.
Space, unlike time, Foucault argues, has yet to complete its process of secularization, and sanctity still plays an important part in the way we divide space. We still divide to inner form the outer, the internal from the external and assign different meanings to different types of spaces depending on their mutual relations.
In "On Other Places" Foucault, as suggested by the title of his article, focuses on those places which bear a "strange" relation to other places by suspending, neutralizing or reversing the relationships through which we can point at them, reflect or conceive them. These "other places" are according to Foucault wither utopia, places that don't really exist, or heterotopias.
A heterotopia is a real place which stands outside of known space. A zoo is an example of a heterotopias because it brings together into a single space things that are not usually together. A mirror, Foucault says, is at the same time a utopia and heterotopias. On the one hand a mirror is a place without place, and on the other it is a real place. And as Foucault says, it the mirror we find ourselves missing in the place that we are.
Foucault argues that heterotopias are a part of every culture, though they are manifested differently in different places and times. A heterotopia can also function differently and in different situations, for example the cemetery which was once in the center of town but is now removed from it. A third characteristic of heterotopias that Foucault mentions is that heterotopias are able to oppose, in the same place, different places (like the zoo or a botanical garden). A fourth principle of heterotopias is the link between a heterotopia and time. A heterotopia separates us from our usual time (Foucault calls this "heterochronic") like libraries which are accumulated time or festivals which are transient. A fifth trait of heterotopias is that they always maintain a system of opening and closing which isolates and connects them from and to their surroundings. The final aspect of heterotopias that Foucault mentions is their role is relation to other places. A heterotopia creates an imaginary order and reason which serve to stress their inexistence elsewhere.