Belgium, a federalized state, geographically consists of three regions, of which only Flanders and Wallonia are subdivided into five provinces each; Brussels is neither a province nor is it part of one.
Brussels-Capital forms a single arrondissement for all 19 municipalities in the region by that name.
The arrondissement of Brussels-Capital (geographically coinciding with the Brussels-Capital Region) is not part of any province and consequently forms its own electoral district.
As the only part of Belgium, the Parliament of Wallonia still uses electoral arrondissements.
Each of these electoral districts take their names from the arrondissements they consist of, usually decreasing in order of population.