By output area (lowest level they publically release census data here). Pattern is as expected, but interesting anyway.
Smallest geographical area that the ONS releases data for. Usually a few hundred people in one, sometimes more.
As for where is where...
1. The area that's majority Welsh speaking (defined here as people claiming to be able to speak, read and write Welsh in the last census) is mostly public sector middle class suburbs, but also, I think, Bryn Adda (furthest east of the oa's) which is IIRC mostly council-built housing. The oa's east of that group with high %'s are mostly council-built as well.
2. The other two areas with high %'s are Maesgeirchen (a big council estate) and Hirael (19th century working class district, gentrified in parts).
3. The two areas with the lowest %'s both have lots of students and the like; the big one by the Menai includes the main Uni halls of residence, the areas in the centre of the seat are more in the way of students renting privately.
4. the oa that includes the main site of the Uni doesn't have a very low % though. That's because it also includes
JMJ. That oa is the one next to the big pale one.
Can give a lot more detail about most of the city if you want.
