The metropolitan area of Brussels is divided into three levels. Firstly, the central agglomeration (within the regional borders), with a population of 1,218,255 inhabitants. Adding the closest suburbs (, ) gives a total population of 1,831,496. Including the outer commuter zone (Brussels Regional Express Network (RER/GEN) area), the population is 2,676,701. Brussels is also part of a wider diamond-shaped conurbation, with Ghent, Antwerp and Leuven, which has about 4.4 million inhabitants (a little more than 40% of the Belgium's total population).