Originating from biological discourses and referring to the necessary reproductive space of species populations, the notion of habitat had been used before the CIAM debates for segregationist town planning politics. After the discovery of the mosquito as the vector of microorganisms responsible for diseases like malaria and yellow fever at the end of the nineteenth century, the supposed size of mosquitoes’ habitat (quarter to one kilometer) had become the width of cordons sanitaires that separated European quarters from the infected local populations. The habitat of an insect had become the measurement for the segregation of human habitats in transcultural modernity.
F.D. Lugard, British colonial administrator, wrote in 1919: “The first object of the non-residential area is to segregate Europeans, so that they shall not be exposed to the attacks of mosquitoes which have become infected with the germs of malaria or yellow fever, by preying on Natives, and especially Native Children, whose blood so often contains these germs. It is also valuable as a safeguard against bush fires and those which are so common in Native quarters, especially in the dry season in the Northern Provinces. Finally, it removes the inconvenience felt by Europeans, whose rest is disturbed by drumming and other noises dear to the Native.” (Home 1997: 138)
One of the most popular zone sanitaires was the green belt. Although the term emerged with Ebenezer Howard around 1900, the planning typology was used in earlier British colonial settlement planning to separate town and country with a building-free zone around the town and to segregate European and non-European settlements. The width of such a green belt differed depending on its purpose and concept. It was argued to be a tool to defend against all things coming from ‘outside’ such as robbery, wild animals, fire, migration, and diseases with the aim to “‘encourage a high standard of living and promote a sense of citizenship, pride and enterprise’.” (Home 1997: 252)
Another planning typology in the discourses of ‘Zone Sanitaire’ was wide streets. Wide streets emerged as a tool for planning and control, because “the narrow streets, the winding alleys, the crowding together of houses, form an insanitary labyrinth, which cannot be efficiently cleansed nor purified by a free circulation of air.” (Home 1997: 90)
Until the middle of the 20th century the cordons sanitaires was a common colonial planning practice. For example, French officials divided the experimental housing complexes of Carrières Centrales, El Hank, Sidi Othman in Casablanca, Morocco, for example, both racially and religiously into developments for Muslims, Jews, and Europeans. The estates for “Muslims” were built far away from the colonial European city center, on the edge of this empty intermediate zone known as a “Zone Sanitaire.” This striking spatial segregation was argued with hygienic and epidemic vocabulary but was also a legacy of the colonial apartheid regime in which Moroccans were forbidden to enter the protectorate city unless they were employed as domestic servants in a European household. Moreover, this also constituted a strategic measure, facilitating military operations against possible resistance struggles. (FA+MH+MvO)

Sources:
Home, Robert (1997): Of Planting and Planning. The making of British colonial cities. London: E & FN Spon, an imprint of Chapman & Hall.