More information about the differences between the APS and the census can be found in a bulletin presenting more detailed results on the Welsh language from the APS from 2001 to 2018.
I gael gwybodaeth fanylach am dueddiadau mewn perthynas â phobl a'r boblogaeth, gweler sleidiau 8 i 31 ym Mhecyn Tystiolaeth Adroddiad Tueddiadau'r Dyfodol Cymru 2021.