After several decades, an increasing number of European cities have been experiencing population growth after a longer phase of decline. This new growth represents not just a quantitative phenomenon but also has qualitative implications for the urban space and the built environment. A juxtaposition of re- and de-densification, as well as changes in land use, in the form of a small-scale spatial mosaic, can be observed. A crucial factor for estimating the relationship between the built environment and demand for it is population density. Increasing population densities may put pressure on sustaining a certain quality of life and on ecological recovery spaces. In this vein, an indicator concept for re- and de-densification will be applied to the city of Leipzig, one of the most illustrative examples of a regrowing city, in order to shed light on the complex relationship between changing human housing demands and their impact on land use. The concept involves measuring population density. Our study has demonstrated that, although similar density changes can be observed in different periods in different parts of the city, they are dominated by different drivers, leading to the formation of different spatial patterns. The results of our study emphasise that regrowth should be understood as a distinctive process because it is distributed very heterogeneously within the city area, with a variety of spatial effects and impacts. The concept allows us to draw conclusions about processes that mitigate, drive or reinforce regrowth, and therefore contributes to a better understanding of this phenomenon and its implications for land use.