The article discusses the concepts of “Marshallian” and “Jacobian” proximity effects. It establishes the basic differences between clusters and other forms of spatial concentration of businesses. Agglomeration effects associated with cluster form of organization of the regional economy are identified. The tools for assessing the factors of geographic concentration, reflecting the influence of agglomeration effects, are presented and examined. The degree of concentration and urbanization for cluster groups of subjects of the Russian Federation is assessed.