section_path: Key features/Power structure
section_name: Power structure
paragraph_text: Power structure
  
  Constitutions also establish where sovereignty is located in the state. There are three basic types of distribution of sovereignty according to the degree of centralisation of power: unitary, federal, and confederal. The distinction is not absolute.
  
  In a unitary state, sovereignty resides in the state itself, and the constitution determines this. The territory of the state may be divided into regions, but they are not sovereign and are subordinate to the state. In the UK, the constitutional doctrine of Parliamentary sovereignty dictates that sovereignty is ultimately contained at the centre. Some powers have been devolved to Northern Ireland, Scotland, and Wales (but not England). Some unitary states (Spain is an example) devolve more and more power to sub-national governments until the state functions in practice much like a federal state.
  
  A federal state has a central structure with at most a small amount of territory mainly containing the institutions of the federal government, and several regions (called states, provinces, etc.) which compose the territory of the whole state. Sovereignty is divided between the centre and the constituent regions. The constitutions of Canada and the United States establish federal states, with power divided between the federal government and the provinces or states. Each of the regions may in turn have its own constitution (of unitary nature).
  
  A confederal state comprises again several regions, but the central structure has only limited coordinating power, and sovereignty is located in the regions. Confederal constitutions are rare, and there is often dispute to whether so-called "confederal" states are actually federal.
  
  To some extent a group of states which do not constitute a federation as such may by treaties and accords give up parts of their sovereignty to a supranational entity. For example, the countries constituting the European Union have agreed to abide by some Union-wide measures which restrict their absolute sovereignty in some ways, e.g., the use of the metric system of measurement instead of national units previously used.