Strictly fashionable neighbourhoods may be divided into
EXCLUSIVE
ULTRA-FASHIONABLE
FASHIONABLE
QUASI-FASHIONABLE
MIXED
EAST INDIAN
HIGH GENTEEL
LOW GENTEEL
EQUIVOCAL
DECIDEDLY LOW
    Of exclusive neighbourhoods there are but few. Piccadilly, westwards from Devonshire House, decidedly takes the lead: His Royal Highness the Duke of Cambridge lends to their neighbourhood the sanction of his preference. The hero of Waterloo makes Hyde Park Corner classic ground; the Dukes of Devonshire and St. Alban's, the Marquis of Northampton, the Earls Cardigan and Rosebery, Lord Willoughby D'Eresby, and a host of our nobility, stamp this locality with supreme bon ton : if wealth can enhance Piccadilly as a place of residence, Miss Burdett Coutts and the Baroness Rothschild divide between them a million charms; but, above all, there is no locality in London commanding a nobler view than that enjoyed from the windows of the mansions in Piccadilly, extending far and wide over the parks, and terminated only by the undulating outline of the distant hills of Surrey.
    Most of the streets that abut immediately upon the parks, overlooking the greensward, are entitled to the rank of exclusive, although nothing can prevent vulgar wealth at times forcing itself into these favoured retreats of fashion, and becoming an eyesore to the whole neighbourhood. .... Arlington Street, overlooking the Green Park, is one of those dear exclusive neighbourhoods : the fine facade of Lord Spencer's noble mansion here attracts general attention. Park Lane is another, vying with Piccadilly in the intensity of fashion. Grosvenor Square, though in a less degree, approaches exclusiveness; while Portman, Cavendish, and Belgrave Squares, must be content to come within our ultra-fashionable category. Of merely fashionable streets, we boast a profusion;  those tributary to the leading squares, borrow from their aristocratic neighbours a lustre not their own; thus George's Street, Hanover Square, on a friend's card or your own, is quite correct, while George's Street, Bloomsbury, is outlawry and civil death!
    In nothing should a man who means to be in society in London be so scrupulous as about his address : life and death depend upon it : let a man study morals, characters, dress, equipage, or appointments, manner, deportment, or amiability, as he will, Baker Street and Russell Square will make all his exertions null and void ... take care that [your location] is situate in Lower Mount Street, Arlington Street ( on the west side, for the east side is only quasi-fashionable), Brook Street (upper) or Park Street, Grosvenor Square. Be very particular about this : eschew streets abounding with brass plates of dentists and doctors, or you are a lost mutton: fly, as you would the plague, neighbourhoods with public-houses at the corners; if a batchelor, a first floor over a jeweller's shop in Bond Street may be tolerated, provided you bring your own man cook and valet; but if a married man, your family is disgraced for ever ...
    The most ridiculous and unnatural, although highly fashionable, alliance between poverty and pretension, so prevalent now-a-days, has give rise to a custom of giving cards from clubs ... you must always avoid fellows who give you the card, not of their residence, but of their club; depend upon it, the leprosy of poverty hands about these fellows ...
    Quasi-fashionable neighbourhoods abound ... avoid the more northerly parts of the populous borough of Marylebone, the new streets and squares to the northward of Hyde Park, and the territories, of whatever descriptions, in the vicinity of Pimlico. The last-mentioned neighbourhood, especially, is proverbially fatal to fashionable expectations; yet many simple-minded persons from the country, opine that,in the neighbourhood of a royal palace, they must be right. ... even royal preference cannot establish the aristocracy of a vicinity famous only for its brick pits and its ale.
    Privy Gardens, May Fair, and Spring Gardens, may probably assert the custom of society in favour of their strictly fashionable character : the two latter, however, have assumed somewhat of a quasi character of late years; the streets secondary to Belgrave Square, and those leading from Piccadilly, are very much in the same condition.
Mixed neighbourhoods are so numerous as to defy classification : one end of a street, as Piccadilly, shall be intensely vulgar, the other shall aspire to the Corinthian capital of society.
    The East Indian, colonial, and merely wealthy circles gather together at the hither-end of Portland Place, and diverge round the Regent's Park, occupying those stately terraces, as new as their own families, and, like themselves, exhibiting fewer evidences of good taste than of magnificence. Harley Street, for example, is the headquarters of oriental nabobs - here the claret is poor stuff, but Harley Street madeira has passed into a proverb, and nowhere are curries and mulligatawny given in equal style. The natives here are truly a respectable praiseworthy body of men; and if it were not for the desperate but unavailing efforts of their wives and daughter to lug them into circles where their wealth excites only envy, and their ostentation only provokes contempt, would be above all praise or blame.
... Of high genteel neighbourhoods, Baker Street, Gloucester Street, Portman Square, the swarm of little streets nestling at the verge of Park Lane and those lying between St. James's Street and the Great Park, may be taken as examples. The people inhabiting this class of neighbourhoods are usually scions of respectable, and distant connexions of noble families, remarkably correct in their stlye of living and equipage, but evidently of slender means; however, they boast this advantage, that an educated taste can do more in this style of living with a thousand a year, than vulgar opulence can with ten times the revenue.
    Low genteel neighbourhoods we need hardly say are drugs in the market. The New Road, Paddington, Pimlico, Bayswater, Clapham, Upper Clapton, may serve as illustrations. Boarding houses abound, furnished lodgings are the staple commodity, and omnibuses pass the doors for your accommodation every five minutes. Hereabouts, if you believe the advertisements, there are always to be found, for next to nothing, "really comfortable homes", "liberal tables" and houses "replete with every convenience" ... French counts and disguised dancing masters preponderate ...
    Equivocal neighbourhoods are those where private residences, shops and manufactories are intermingled in heterogenous confusion. Lambeth, the Borough, Vauxhall, and the regions generally included in the "over the water" category belong to this unenviable description.

The World of London, by John Murray, in Blackwoods Magazine, July 1841

see also Henry Mayhew in The Criminal Prisons of London - click here