That is incorrect. It is actually 275,000. Strangely on Wikipedia as well as other sources, unless that excluding Washington, Houghton etcSunderland itself is 175k. http://en.m.wikipedia.org/wiki/Sunderland,_Tyne_and_Wear
If you include the Borough then fair enough yes it increases. I'm unsure why you're mentioning catchment area, Burnley have a greater catchment area than we do, the problem is they have more competition. But that's life. We benefit from our location in some ways but at the same time there are disadvantages.