Energy and urban form. The growth of European cities on the basis of night-time brightness

The European urban system has experienced significant transformations over the last two decades, affecting both the system's articulation and hierarchy, and the morphology of urban areas. The sources of information on land use, although increasingly precise and exhaustive, present some limitations when it comes to identifying and quantifying this development, particularly due to their sporadic nature. In this context, the advances in the availability, precision, territorial coverage and recurrence of night-time satellite images offer new opportunities to assess the transformation of land uses. Under the assumption that there is a direct relationship between light emissions and the level of urbanisation, the present study identifies the development of the European urban system between 1992 and 2012. In this respect, the level of brightness suggests that the extension of urban land uses has been much greater than those calculated by using other sources, such as aerial photography or planning regulations. The contrast with these sources demonstrates that, even though night-time images are subject to significant limitations, their use can have advantages in the explanation of new patterns of land use. Thus, brightness could contribute to a more complex picture of the urbanization process, measuring not only the artificialisation of land but also the spread and intensity of urban uses of space.