Abstract <p>The article studies the relationship between the categories of density and concentration with a case study of the hierarchy of urban settlements with respect to population density in Russian regions. The methodology compares the population density of a region as a whole with the share of the region’s area occupied by settlements, as well as ideal distributions according to the Zipf rank-population function (Zipf’s Law) with the actual hierarchies of urban settlements, both for the territory within the borders of the Russian Federation in dynamics since 1897 and for individual regions. The results indicate that at certain stages of their development, settlement systems move towards fulfilling the rank-size rule and become less contrasted, while the level of concentration decreases (urbanization in breadth). After reaching a mature level, with the onset of agglomeration processes, systems again cease to conform with the Zipf formula and become more contrasted (urbanization in depth). In general, in regional systems with high population density and a significant number of urban settlements, the rank-size rule is observed better than in systems with average density values. In systems with low population density, the rank-size rule comes into play again. The heterogeneity of Russia’s space in terms of population concentration is shown at various scale levels.</p>