From the 1950s to the present, the borough's history has been dominated by its population growth and urbanization, along with the problems that come with it. Before 1970, the area still had various types of flora including forested hills, ponds and other surface water, grasslands and more. Chinampas and other farmland still existed as well. In the 1970s, waves of migrants from other parts of the country began to move into the borough. This prompted the building of a number of large apartment complexes including Unidad Vicente Guerrero, Unidad Ejército de Oriente, Unidad Santa Cruz Meyehualco, Conjunto Urbano Popular Ermita Zaragoza and Unidad Habitacional Ejército Constitucionalista. By 1980, all of the land that could be developed legally was, but the population continued to grow. In the 1990s, the borough had growth rates of over 100% according to INEGI. By 2000, the population of the borough accounted for over 20% of the total of the Federal District, the largest in population. Now almost all of the land in the borough has been urbanized, with only the highest elevations and a few family farm plots without buildings. The only green spaces are parks controlled by local or federal authorities, where various types of trees can still be found.