  In Mexico, 25 per cent of the urban population now lives in informal
settlements with varying degree of depravity. Although some informal
neighbourhoods have contributed to the upward mobility of the inhabitants, the
majority still lack basic services. Mexico City and the conurbation around it,
form a mega city of 21 million people that has been growing in a manner
qualified as "highly unproductive, (that) deepens inequality, raises pollution
levels" and contains the largest slum in the world, Neza-Chalco-Izta. Urban
reforms are now aiming to better the conditions in these slums and therefore it
is very important to have reliable measurement tools to assess the changes that
are undergoing. In this paper, we use exploratory factor analysis to define an
index of depravity in Mexico City, namely the Slum Severity Index (SSI), based
on the UN-HABITATs definition of a slum. We apply this novel approach to the
Census survey of Mexico and measure the housing deprivation levels types from
1990 - 2010. The analysis highlights high variability in housing conditions
within Mexico City. We find that the SSI decreased significantly between 1990 -
2000 due to several policy reforms, but increased between 2000 - 2010. We also
show correlations of the SSI with other social factors such as education,
health and migration. We present a validation of the SSI using Grey Level
Co-occurrence Matrix (GLCM) features extracted from Very-High Resolution (VHR)
remote-sensed satellite images. Finally, we show that the SSI can present a
cardinally meaningful assessment of the extent of the difference in depravity
as compared to a similar index defined by CONEVAL, a government institution
that studies poverty in Mexico.
