The thin yellow line winds north from Regent's Park, outlining the terraced, paired and detached villas of the select roads of Hamp stead, Primrose Hill and Belsize Village.
Between them, dark red delineation dominates. Only in Kentish Town and Somers Town does the chilly blue end of the spectrum intrude into Charles Booth's colouring of London by its inhabitants' financial standing.
His Descriptive Map of London Poverty, drawn up in 1889, has long been recognised as a uniquely valuable tool by researchers into Victorian social history. But, says one of those who have used it, it is inaccessible.
"People know about the map, but don't actually look at it," is the comment of David Reeder, from the Victorian Studies Centre at Leicester University.
Now, however, they can, thanks to the enterprise of the London Topographical Society, which has reprinted the few-sheet, six-inch-to-the-mile, seven-colour cartographic survey as its 1984 publication.
An appropriately large-scale introduction from Dr Reeder accompanies the map, which he believes to be of wide public interest, over and above its use to anyone studying or teaching the period.
"It is quite phenomenal in a way how all these different levels of wealth and poverty have been reproduced. The map has the kind of instant impact that bowls people over."
Prosperous Hampstead, wrote Booth, was the "alpha" of his survey, certain areas of the East End the "omega".
"Taking the entire population of London, Booth found just over 30 per cent in poverty and about 70 per cent in comfort, a serious state of affairs," expands Dr Reeder. It was worse than a preliminary survey of East London had indicated, "but not as disastrous as had been widely supposed".
Booth, he explains, was a wealthy London businessman who set into being a major survey which extended beyond poverty to industry and religious influences in the capital.
"Booth was in the line of many self-styled private investigators, and his survey is best regarded as the culmination of a Victorian statistical movement preoccupied with acquiring information mainly about the habits of life of the poorer sections of urban society."
Where his map was so remarkable was in the sophistication of its recording of the gradations of poverty/ prosperity. The seven colour codes mounted from black — "lowest class, vicious, semi-criminal"—to yellow— "upper middle and upper classes, wealthy".
In between came the very poor, in chronic want, defined by dark blue lines, the pale blue poor (18s to 2s a week for a moderate family), the purple mixture of poor and comfortable, the pink fairly comfortable - "good ordinary earnings" - and the red well-to-do middle classes.
Poverty, Booth considered, ended only when light blue had turned to purple, with true working class comfort arriving as the purple shaded to pink and the heads of households enjoyed such jobs as clerks or mechanics.
Typical of the red householders were caretakers, police sergeants and shopkeepers, while in the yellow homes, rated at £100 or above, three or more servants were employed.
Conditions just south of the Euston Road in the decade after Charles Booth compiled his Descriptive Map of London Poverty— a case, surely, for black delineation.
Picture courtesy of the Camden Local History Library at Swiss Cottage.
He drew his own conclusions from it, notably that, the better classes were stead ily moving out to the; suburbs, that the poorest people were "trapped" into slum cul-de-sacs cut off by. railways and canals.
And he saw solutions— cheap transport to ease the, flow to the suburbs and Government action to move the poor out of the worst districts—"a radical surgery to cure the malfunctions in the physiology of London 's social body", says Dr Reeder.
And he sums up the map as "a still picture, a snapshot taken at one moment or period of time of a city whose changing social complexion was of engrossing interest to Booth and his ; team".
What would the map-maker's conclusions be today?
He'd find changes, certainly, if he set out once more to visit what 95 years ago were the poorest streets on that section of the map covering the northern half of the present borough of Camden.
The slums delineated by his black ink in Somers Town must have hung on. many consciences. The St Pancras Housing Association and Camden Council are the landlords there now, of replacement blocks of a vintage which currently requires their renovation.
In Kentish Town, too, streets as well as slums have been wiped off Booth's map. The dark blue Litcham Street, off Weedington Road, and Preston Street, off Maiden Road, are history now. And while St Leonard 's Square remains, the tenders of the neat, rose-filled front gardens might resent a light blue categorisation.
Only a few hundred yards away, there have been equally significant changes, but the loss is of property at the other end of Booth's social scale. The red villas of Maitland Park are no more than a memory, beneath more council fiats.
West of Haverstock Hill, red turned to yellow through the Belsize streets, newly-built Fitzjohn's Avenue and the stuccoed terraces leading to Swiss Cottage.
Booth, confident in his designation, probably never saw the gracious brick villas, of, for example, Strath ray Gardens. Today, the entryphones and rows of bells of multi -occupation have extended even here, beneath the terracotta garlands, the elaborate balustrades and the patterned and coloured leaded lights whose cleaning must have kept the three - servants - per - house well occupied.
The mapping stopped just short of Hampstead Village, but encompassed much of West Hampstead (red and pink principally, though Cleve Road merited yellow), all of St John's Wood and Bloomsbury.
Dr Reeder's conclusion of its value cannot be bettered: "At one level it gives us an indelible impression of the complex social patterning of a mature metropolis; at another level it provides a ready reference guide to the social geography of nearly every corner of London 's metropolitan development in the 19th century."
Individual copies of the Descriptive Man of London Poverty cost £12. from Dr Ann Saunders. London Topographical honorarv editor, 3 Meadwav Gate, Hampstead Garden Suburb (phone 455 2171). Membership of the society is £5 a year. which includes the annual publication.
Booth's concern for London 's poor was not unusual, Dr Reeder points out. "A social trigger affecting his initiative was the sense of crisis about the condition of London which permeated discussions of its social prob lems in the 1880s."
He had joined in those discussions, as an associate of the "socially conscious and influential group of people" associated with the ' East End settlement of Toynbee Hall.
And his efforts to establish the scale of the problem of poverty were founded, Dr Reeder suggests, in the con cern evoked by the contemporary flush of writings on '"the implications for society of the existence of great “poverty in the midst of plenty”.
"Middle class anxieties were fuelled by the descriptions of the poor, or sections of the poor, as a brutalised and degenerate race of people, the victims but also the agents of the deteriorating forces in city life. It was a somewhat apocalyptic vision of the future, but having a basis all the same in the realities of the metropolitan economy."
What of the realities of Booth's facts, on which he coloured in the map—originally 25-inch-to-the-mile Ordnance Survey sheets now housed in the London School of Economics and the Museum of London.
Principal initial information came not from direct inquiry by his team of investigators but from the details reported by School Board attendance officers, whose duties included collecting personal information about families with school-age children, and from what was generally known about occupations in each street, the habits and life of the people and the appearance of the houses and their occupants.
But the team also took the investigations further, talking to clergy and lay helpers, school teachers and local worthies. Finally, Booth, or an assistant, personally visited the poorest streets.
Notebook after notebook was filled with information, sometimes even detailed accounts of individual houses, to confirm that the distinctions drawn by the different colours did match differences in social class.
Booth's work, Dr Reeder continues, showed up three specific aspects of social patterning in Victorian London—the continuing tendency for the wealthy to inhabit certain quarters, the much more even distribution of the well-to-do and the concentration of poverty in the old industrial and dockland quarters.
But, in detail, the pattern was far less straightforward, as the poverty map was uniquely able to illustrate. Some of Booth's contemporaries regarded the detail simply as revealing a city in chaos; to the mapmaker himself the aim was to "reveal the regularities in the; metropolitan condition, to expose its orderliness, and: thus, to make London comprehensible as a city".