Throughout the paper, the terms informal settlements and slums are used interchangeably, since informal settlements are often referred to as slums and vice versa in previous literature. Though by definition, not all slums would be considered as informal settlements. However, according to UN-HABITAT's definition informal settlements are always considered to be slums by virtue of the lack of tenure security. Moreover, the great majority of informal areas are occupied by relatively poor residents and will usually have at least one additional form of deprivation.

The work is the product of a collaboration with CODEV (Centre pour la cooperation et le développement) at the EPFL (Ecole Polytechnique Federale de Lausanne, Switzerland) and CRD-PVS (II Centro di Ricerca e Documentazione in Tecnologia, Architettura e Città nei Paesi in via di sviluppo) at the Politecnico di Torino. Both are involved in research activities in the fields of habitat in developing and emerging countries.

Coherent with the common vision of the importance of the slum question when talking about urban planning and social development, the aim of the work is to actualize the analysis of the phenomenon, using the technology we now dispose, through a number of case studies in several emerging and developing countries, and comparing it with the traditional models used in order to achieve some relevant conditions, either positive or negative, that should be gathered to improve the general studies on slums.

Traditionally the analysis is based on socio-economics characteristics hich brings to the prescription of 'good practises' given to the communities' stakeholders by the International Organizations; in the proposed case the method is physiographic indeed, based on digital images, analysing the geo-physical characteristics and it has the aim of improving the traditional one.

The goal is translated in the research of a taxonomy which could give order to what is born as a complete disorder, without any rules of architecture, urban planning, social life or economy, but which, if analysed, represents a special development and will of the inhabitants.

In order to do this the work doesn't want to start from a classical analysis of the informal characteristics of the different settlements, but from their 'urban shape', that is from how the first inhabitants got appropriated of small amounts of lands just to get a house where to live, a place where to work, public spaces where to meet and then they spread to the contiguous lands, following not-written rules or simply intuitions.

This implementation of information about slums can be useful or planning and monitoring urban poverty alleviation programs, as slums are directly related to poverty and they are home to a growing )roportion of dwellers thanks to the rising urban population and consequent increasing in urban poverty.The systematic quantification of slums requires methods to identify and define them spatially in a consistent manner in support of geographical targeting in slum intervention programs. Further, considering the rapid change in the structures of such settlements as a result of expansion, infill, relocation and extension, this kind of technique could help in slum monitoring. For these reasons, there is a growing interest in developing and exploiting robust approaches for collecting information on slums.