An area of 200,000 people would typically have about 80,000 households, of which maybe 10% (at most) would instruct a professional carpet cleaner in any given year. If we assume an average ticket price of £100 for each job, the total value of residential carpet cleaning work in your area might be £800,000. This is a high-end estimate - more realistically it might be half this number in the current economic climate - about £400,000. On this basis your area should be able to support the equivalent of 10 full-time carpet cleaners. If you factor in commercial work as well, you could possibly add another 5 full-time carpet cleaning operators for a typical conurbation of that size.