Over the last few decades, within the framework of remarkable urban expansion accompanying a real-estate boom in Spain, it has been medium-sized cities that have registered the most drastic changes in morphology. Currently, about 50% of urbanised land was developed after 1980. Historically compact and dense urban structures have been transformed, with new urbanised spaces expanding into the outskirts. High land consumption has created sprawling, fragmented and scattered urban areas. These are new, more complex and multifunctional urban structures, and there has been a change in the scale of urbanisation, in the forms and in the resulting urban landscape. However, the growth model which has caused these transformations is defined by hardly sustainable land-use patterns. The number of medium-sized cities has increased by around 50%, while the number of houses built has grown by 109% and developed land by 87% between 1981 and 2021. This paper analyses these recent dynamics through the statistical treatment of growth patterns and their cartographic analysis using GIS technology. The significant modification of urban forms at this scale in the Spanish urban system is confirmed. The paper also reflects on the lack of sustainability in the prevailing model with respect to the 2030 city strategy.