Territorial sustainability is often related to the land cover and local resources. Land cover data are used more than other remote sensing and digital photography methods for determining and analysing the information collected from a certain region. However, having the dynamic evolution of urban areas in developed countries, such methods and indicators should be considered in order to assess their development directions and sustainability. Between 1990 and 2012, Paris Metropolitan Area (PMA) recorded increases in urban land due to the continuous expansion of the built-up area. In this study, we proposed to calculate the Metropolitan Area Sustainability Index (MASI) by using a GIS procedure, incorporating the land cover of PMA for two reference years (1990 and 2012). Six indicators were selected for the PMA territory based on which the City Index was calculated. Two correction factors, namely the Environmental Capacity of Development and the Land Restriction for Development, were defined in order to develop the MASI of PMA. High MASI values were found in the north-central, southern, and western parts of the PMA, while lower values were identified in the peripheral areas. This study suggests that the proposed method is reliable for the territorial sustainability assessment. The methodology and original maps represent useful tools for future urban planning in large cities.