Each constituency elects one Member of the Senedd (MSs) by the first past the post electoral system, and the region as a whole elects four additional or top-up  MSs, to create a degree of proportional representation.
The Senedd is composed of members elected by constituencies using a first-past-the-post system, with an additional four seats allocated through a top-up system to provide a degree of proportional representation for the entire region.