[1] It consists of four agglomerations which form the four corners of an abstract diamond shape: Brussels, Ghent, Antwerp and Leuven.

The other major Belgian metropolitan areas that are in relative proximity to the national capital (that lie within a radius of approximately 50 kilometres (31 mi) around Brussels) are the exclusive competence of the regional authorities.

The name refers to the geometrical shape of a diamond, corresponding to the location of the four cities and surrounding metro areas, which are among the most urbanized and industrialized – and prosperous[6] — in Belgium.

[7] It also links its peripheral area for more than a hundred kilometers, exceeding Flanders, to the international and global economy.

[7] The economic activities in the relatively larger metropolitan areas are distinct, with an emphasis on industry in Antwerp, mainly because of its major port, versus on administration for Brussels, as Belgian capital and its function for the European Union and NATO.