The reason for reviewing these boundaries is that over time, the number of electors in different areas changes, perhaps because a new housing estate has been built.
Y rheswm dros adolygu'r ffiniau hyn yw, dros amser, bod nifer yr etholwyr mewn gwahanol ardaloedd yn newid, efallai oherwydd bod ystâd dai newydd wedi'i hadeiladu.