There are times that I wish all my English ancestors came from Somerset - many of the Somerset records are readily available on the internet, for free. Many people have voluntarily transcribed parish records and uploaded them for the benefit of all who wish to use them.
I wish such a thing happened for London records. But London is probably also different because I imagine its population was more transient - the nature of a big city (even though it was much smaller then) is different to a small town.
Despite this presumed transient nature I always use Google maps when doing my family research. I work on the assumption that most people did not move around much (apart from huge moves, such as to Australia). So whenever I find records which may be for the ancestor I am working on I plot the locations on Google maps to see how far apart they are. It's an inexact science but one that can be quite helpful.
I've been using this approach with my ancestor James Ball. According to family information he was born in London in 1814 to Thomas and Sarah Ball. I cannot find a birth record for a James Ball born to parents with those names in London in 1814. I can find one with a birthdate of 19 December 1812 though, who was baptised, along with a sister Eleanor (born 17 June 1817), at St Mary Mounthaw on 23 November 1817. Is this my James? I don't know. James and Eleanor's father was listed as a corn porter, and their address was given as Old Fish Street Hill.
In the 1841 Census James is living with his children (his wife Susannah isn't at that address at the time - not sure where she was) in Little Carter Lane (the eastern end of what is now known as Carter Lane). He is listed as a book binder.
In the 1851 Census the family is living at 20 Little Carter Lane. James is listed as 38 years old - I'm not using the age given on the 1841 Census because the ages for persons over 15 were rounded to the nearest 5 years - not very helpful to the family historian. If he was born in December 1812 this age fits with the census date of 30 March 1851 - he would have been 38 years 3 months and 11 days old. His place of birth is listed as Middlesex. This fits with a birthplace of somewhere around Old Fish Street Hill.
When James and his family emigrated to Australia in 1857 on the Matoaka he was listed as 43 years old (fitting with a 1814 birthdate), as a carpenter (not really what I would describe as the occupation of a book binder) and his place of birth as Higate (sic) Middlesex. His parents are listed as Thomas and Sarah, living at Fenchurch St, London. His religious denomination is listed as Independent - this would mean he wasn't Church of England, and if he was baptised in a non-conformist church then those records may not be available - a possible reason why I can't find a birth record for him in 1814.
So, the places we have are: (a) Old Fish Street Hill, (b) Little Carter Lane, (c) Fenchurch Street, and (d) Highgate. If we plot these locations with Google maps, (a), (b) and (c) are very close to each other and Highgate is an outlier, about 6kms away.
Can we assume that if the Immigration Board got his occupation wrong they might also have written down the birthplace incorrectly? The Agent's immigration list also has his occupation as Carpenter, but is less specific with the place of birth, giving only Middlesex. I tend to think, going on the fact that (a), (b) and (c) are all in the same neighbourhood, that the 1812-born James Ball is my relative. I think that the "Highgate" information is wrong, as is his occupation as "Carpenter" - certainly he worked as a book binder in Australia as well as in London. I can't be sure it is him, but to me there seems a reasonable possibility.