The urban-rural interface has usually been studied from the point of view of cities with different sectoral interests and very little from rural perspectives. Nevertheless, these kinds of areas need to be studied from both points of view and from comprehensive approaches that could reflect their complexity. Thus the work is oriented to make a comparative analysis of two main approaches to dealing with the rural-urban interface in a Latin-American context: one coming from towns and the other from the countryside, where both of them include the sustainable and a territorial perspective of development. The analysis has taken into account economic, social, environmental and political-institutional issues, as well as urban-rural interactions. Results underline some contributions of such approaches to theory and practice of planning and management of these spaces; such as the value of a complex systems view, planning in different spatial scales and time scenarios, the territory as a support of socio-economic and environmental processes and the role of local actors in this transformation. To conclude, rural development has been arising as an emergent field where medium and small size towns play an important role in linking production with local and global markets and enforcing rural-urban relationships in urban systems.

Mexicali has an important economic role within the state of Baja California, Mexico, and its urban economic dynamic has been a central piece of regional development in the Mexicali valley. This has produced a rapid urbanization of the rural-urban interface, which has intensified energy, material and population exchanges between the central city and its hinterlands. Such a dynamic has produced urban sprawl and a fast restructuring of the urban regional spatial development. Thus, the purpose of this paper is to analyze the spatial dynamics of the rural-urban interface of Mexicali, from 1990Mexicali, from -2005. Urban spatial expansion was analyzed by satellite images, LANDSAT TM5 and LANDSAT ETM7 taken in the dry season, to identify land use changes and the physical expansion of the urban area over the last 15 years. Results have showed that Mexicali's urban area has expanded by around 32 km 2 , which means an increase of 34% during this period. Meanwhile small cities located in the hinterlands have experienced lower rates of population growth and physical expansion. Some small cities have been absorbed and others have developed over urban corridors to the central city. Changes in spatial patterns of urban structure have been accompanied by the evolution of urban functions and special interactions between the central city and its hinterlands. Lastly, the urbanization process is still in progress, but there are also evidences of urban sprawl in the hinterlands.

Among the problems that cities face are rapid growth and dynamics in the peripheral and suburban areas of medium size towns, characterized by mixtures of residential neighborhoods and squatters' settlements with wide differences between levels of urbanization and public services. There is also an important flow of commuters, loss of productive and conservational lands and management among several municipalities. Thus the objective is to present a methodological proposal to address the rural-urban interface from a sustainability perspective. To achieve this, six issues were considered: migration and socio-demographic changes, economic growth of the city-region, urban mobility and residential change, settlement morphology and functions, use and depletion of resources and urban and environmental management.

Tijuana, Playas de Rosarito and Tecate form a recent metropolitan area, characterized by high rates of population growth and economic activity, in a short period of time it has become the fifth biggest metropolitan area in Mexico. This fact has influenced federal, state and municipal governments to initiate a series of meetings in order to make a proposal for the planning and management of the area. The proposal includes an integrated assessment about current conditions of social, economic and environmental issues in order to develop some strategies for its management. Then we deal with environmental issues in order to achieve sustainable development concerning water uses, energy, risks, solid wastes, land uses and conservation areas. After the assessment, there were some strategies suggested for resource management within inner city, periurban and suburban fringes. Finally, the paper points out some practical shortcomings related to planning and management: the lack of coordination among public institutions, a weak implementation of municipal regulations, scarce environmental data and the implementation of monitoring. As well as a fragmented planning with remarkable priorities differences that have not matched in time, space and financial resources, at all.