It is interesting where the players of every team have been brought up as children as how it has changed over the years.
In the past the Boro always had 1 or 2 Scots (say Souness & Murdoch, McAndrew and Hamilton, Slaven and Hendrie), then possibly an Irish player, then a few more from County Durham/Northumberland, then one from the North West and possibly one from Yorkshire/North Midlands, but always a few from the Teesside area, sometimes half the team.
Then in the Robbo era came 50% from overseas - not so many now directly from overseas (Dijksteel possibly and Morsy and Stojanovic) we still have some local players (Fry, Wing, Pears) and an Irish player, no Scots, two Yorkshire, one other North East, one from Manchester, one from Birmingham and a large number from London area. I suspect the resources for developing children into footballers is very good in London and the advantage that say the North East and parts of Scotland from a rich heritage of developing professional footballers has gone.