This chapter presents some of the urban conditions and policies that have shaped Mexico City's environmental problems, as well as the most serious natural risks it has experienced, particularly in its recent history. It begins with a description of the most salient features of urban expansion in the city in recent decades, and how this has occurred in various parts of the metropolitan area, to analyse its patterns of major population growth, since these factors have clearly influenced the two problems set forth below.

Expansion and sprawl of the urban area

Urban growth entails the physical expansion of a city's urban area (the surface or land it uses, while urban area comprises the political-administrative units), as well as the increase in its population. It also involves the transition from the predominance of agricultural activity, or natural areas, to the secondary and tertiary sectors (CONAPO & SEDESOL 2012: 11). This growth or physical expansion is generally accompanied by tensions and conflicts between agricultural land use in the natural or environmental capital area, and urban land use. In Mexico, these tensions are compounded by the issue of land tenure, characterized by a specific combination of private, public and communal or social ownership.

One available source of information in Mexico for the study of the urban area is population and housing censuses, which separate demographic and housing data into different geographic scales: (1) states; (2) municipalities or alcaldías; (3) localities; (4) basic geostatistical areas; and (5) blocks. The basic urban geostatistical area refers to the subdivision of municipalities or alcaldías and allows the formation of primary sampling units and the organization of statistical information.

Table 6.1 presents information on the size of the urban area in the Mexico City Metropolitan Area (ZMCM) for 2000 and 2020. For further analysis, the metropolitan territory was divided into four parts, which are also used in Chapters 2 and 3: (1) central city; (2) the remaining Mexico City alcaldías; (3) municipalities on the inner periphery; and (4) municipalities on the outer periphery.

The number of basic geostatistical areas in the ZMCM experienced a relative increase of 18 per cent from 4,994 to 5,875 in 2020. The urban area of the ZMCM totalled 2,111 km2 in 2000, rising to 2,362 km2 in 2020, meaning that during that period, it expanded by 251 km, equivalent to a 12 per cent increase (Map 6.1).