A continuation of the Northern Irish Parliament

[Pete Whitehead]

I don't know how that got changed to Old Park(sic) on the map - you'll see in the accompanying text I was referring to that seat as Cavehill

[East Anglian Lefty]

I suspect that seat size plays a fairly significant role in how assured or otherwise a unionist majority is. My working assumptions are that:

a) The unionist vote splits more ways than the nationalist vote (especially if you include the Alliance, because even when they aren't drawing from the unionist pool, they're strongest in historically unionist areas);
b) Whilst there are monolithically unionist and monolithically nationalist areas, the monolithically nationalist ones are probably slightly more monolithic and
c) The monolithically nationalist areas tend to be closer to predominantly-unionist areas whose votes they can swamp, whereas most of the monolithically-unionist areas are wasted in North Down and Antrim.

So if you break it down to DEA level or thereabouts, unionists have the advantage because they're a) more numerous and b) more equally distributed. It's less true when you more or less double the size and can just about drown a DEA in votes from the opposing camp, or at least half a DEA. By the time you get to Westminster constituency, it's much easier for nationalists to outperform their population share without having to draw particularly odd maps.