It is carried out every 10 years and provides the most detailed picture of the entire population, with the same core questions asked to everybody across Wales and England.
Caiff ei gynnal bob 10 mlynedd a hwn sy’n darparu’r darlun mwyaf manwl o’r boblogaeth gyfan, gan holi’r un cwestiynau craidd i bawb ledled Cymru a Lloegr.