All electoral systems that provide for single-member constituencies or multi-member districts rely on the careful drawing of electoral boundaries. Issues of reapportionment and boundary readjustments are essential to ensure equality of the vote. In a number of CoE member states (e.g. Bosnia and Herzegovina, Bulgaria, Spain, and Turkey), however, there is an extremely uneven distribution of seats among constituencies based on the number of citizens or registered voters, making readjustments urgent.