Elections to the Senedd and local government have always operated differently to elections of Members of Parliament, but the differences have become more pronounced over time.
Mae etholiadau i’r Senedd a llywodraeth leol wedi bod yn wahanol bob amser i etholiadau Aelodau Senedd y DU, ond mae’r gwahaniaethau wedi dod yn fwy amlwg dros amser.