The current metro area population of Cardiff in 2023 is 488,000, a 0.62% increase from 2022.
Barry , Penarth ,is within this figure.
https://en.wikipedia.org/wiki/Tyneside#Settlements
This is the greater Newcastle urban area
Newcastle , Gateshead, North Tyneside etc
A continual , joined urban area about 9 miles along the river Tyne to the sea
It's one of the uks biggest urban areas and has a population of 800 000
Cardiff doesn't have a metropolitan area really , it's just Cardiff
If you look at a similar map as the above with regard to Cardiff it's 8 miles till you get to Barry , 12 miles till you get to pontypridd and 12 miles to Newport
Clearly these are not part of Cardiffs built up area and are not joined at the hip like Newcastle is joined to Gateshead and North Tyneside
For administrative and investment purposes it's said Cardiff Metro is 1 million people but that includes Newport, Barry , Pontypridd , Caerphilly etc
Which are obviously not thought of as Cardiff by most people down this way
If you go to Newcastle you can tell its a bigger place than Cardiff by its railway station , arts , music and entertainments scene , the fact it has an underground trains system and driving around the place its clearly a big city with lots and lots of districts