While Pam is looking about ...
There were some (recognised as rather flawed) pieces of research done on prostitution in the Victorian era. The intended point of the research was generally to identify and prevent to spread of sexually transmitted diseases - I have them around somewhere in a drawer and can dig them out if anyone is interested.
As was mentioned, dock areas, and military establishments were major concentrations of prostitution and brothels in the 19th century, but in London (which I know best, historically speaking of course!) there are certain areas that were infamous and well-known and catered for different classes (and of both sexes)
In the research, there were various areas pinpointed in such places like Portsea and the London dock areas and some streets were mentioned that were known and seemingly tolerated by the authorities. The research named streets as well as establishements - looking at the censuses from around the time of the research it is 'somewhat' obvious in some cases - named public houses often had younger and not so younger single women 'lodging' with the noted occupations such as needlewoman, bar helper and the like. None that I saw gave the occupation as prostitute. Other establishments which were named which I found on the census often had several family units, some seemingly husband wife and children whilst sharing was a group of women of varying ages and occupations such as, again, needlewoman, nurse etc.
All in all it was a lot of guesswork and not as obvious as you might think.
Apart from those areas of concentration, prostitution was apparently fairly common especially for single women with no other avenue of income. I suppose many of these women would not be obviously prostitutes on the census.
Having said that, it's a difficult subject and one should not jump to conclusions about needlewomen and the like ...
Biker