It should be further divided.
Yeah I agree. Just look at the latest UK general election, and the latest Northern Irish election maps:
It seems to me that, with the exception of West Belfast, you can draw a very clear border between the unionist and nationalist parts of Northern Ireland. So, my proposal would be to partition northern Ireland into "Northwest Northern Ireland" and "Southeast Northern Ireland". Then the former remains part of the UK with a very large unionist majority, while the rest, which has a majority of people who want to go with Ireland, can do so.
The actual distribution is not nearly as neat.
Poll
