I’ve mentioned that I am very visually oriented, and also (what is probably obvious without me pointing it out again) I have more than a small dose of OCD. Which means I can’t let things go until I’m satisfied. So the research I do for my novels is painstaking. And also, to me at least, tremendously interesting.
I always find the best possible maps for the location that I’m writing about. For Gilded Hour I found maybe a dozen maps published between 1880 and 1885, but only one of those really suits my purpose, so that while I’ll consult many different maps, one becomes my source map. The map I’m using was published in 1885, which means that it was most likely compiled over 1883-84. Manhattan is divided into twenty-four plates (at the top of this post is a small detail from Plate 5, with my annotations).
An example of a supplementary map is the Sanitary Map and Social Chart of the Fourth Ward of the City of New York, which accompanies a detailed report of the living conditions.
Report of the 4th Sanitary Inspection District made to the Council of Hygiene of the Citizen’s Association by E.R. Pulling, M.D., assisted by F. J. Randall. Report of the Council of Hygiene and Public Health of the Citizens’ Association of the New York Upon the Sanitary Condition of the City, second edition. New York: D. Appleton & Co., 1866.
This map is far too early for a novel set in 1883, but it is very useful anyway. It helped me understand the real conditions in the tenements by providing actual data. To be clear, it wasn’t the map so much as the website put together by Peter Baldwin at the University of Connecticut that provided insight. The project is called The Fourth Ward: Life and Death in New York, 1860-70. The website includes high resolution, annotated images of the map itself, as well as the actual report submitted by the Citizens’ Association researchers, also annotated. Consider this short excerpt:

click for a full-sized image
The diagram on the opposite page represents an area eighty yards long and fifty yards wide, including the cul-de-sac at the termination of Cliff Street. It illustrates the proximity to crowded habitations of offensive and dangerous nuisances, often observed in the lower part of the city. The diagram presents an accurate ground plan of each tenant-house which it embraces. Within this space are 20 dwellings occupied by 111 families, and having a population of 538 persons. A soap-and-candle factory, a tannery, and five stables, in which are kept not less than 30 horses, are also wholly or partially included within its limits.
A, B, C, D, E, are tenant-houses fronting on Vandewater Street. An alley four feet wide running through C forms the sole communication with the five tenant-houses F, G, H, I, J, which open into the small court R, in which stands their common privy, f, situated within three feet of the hall door of one of the houses, which is constantly pervaded by its noisome odor; c, d, e are privies situated immediately under the windows of houses F, G, H; a, b are privies belonging to the tenant-houses A and B; K, L,M, N, are tenant-houses standing back to back with two of those in the court above mentioned and with three stables to which access is had from Vandewater Street. The position of two stables fronting on Cliff Street will also be observed. The soap-and-candle factory, whose frontage is shown in the cut, is a very extensive one, and its emanations vitiate the atmosphere for a considerable space around.
T, T, T, represent a series of tan vats, in the rear of a leather factory on Frankfort Street, which generally contain a large number of green hides in a very offensive condition. The peculiar stench from this source is usually quite perceptible through the entire area shown in the engraving.
This locality lies on the borders of a former marsh known as “Beekman’s Swamp.” The appearance of every inhabitant of this region indicates a low and vitiated condition of the system, rendering it specially susceptible to adynamic forms of fever, which, during epidemic visitations, have on several occasions spread with terrific rapidity through the entire quarter. Typhus fever has prevailed during the past year to a considerable extent in some of these houses, while small-pox has been rife in the tenant-houses on Vandewater Street. It has been observed that scarlatina is especially malignant and fatal here.
Things get even more interesting when you can look at the census data for a particular street or block in conjunction with a detailed map. I’ll post about that in the next couple days.