I want to know the answer to the following question:
What other city merged with Southampton after the 2001 census?
All the background I'm provided with is that "In the 2001 census Southampton and Portsmouth were recorded as being parts of separate urban areas, however by the time of the 2011 census they had merged to become the sixth largest built-up area in England with a population of 855,569.". Is that enough to answer the question?
Answer: yes