## Overview

In 1992, Rusty Dodson and Waldo Tobler digitized John Snow’s cholera map. Unfortunately, they did not include the names of roads (e.g., Broad Street) in their data set. While not strictly necessary for analysis or visualization, having the names can be useful so I appended the actual street names from the map to the roads data set.

Before discussing the details, some discussion of the structure of roads is warranted. The data contain 1241 pairs of x-y coordinates that define the endpoints of straight line segments used to describe some 528 numerically identified “streets”.

>   street n        x        y id      name
> 1      1 2 16.73800 18.69600  1 Map Frame
> 2      1 2 17.66000 18.71200  2 Map Frame
> 3      2 2 14.46200 18.65500  3 Map Frame
> 4      2 2 16.73800 18.69600  4 Map Frame
> 5      3 2 12.79388 18.61613  5 Map Frame
> 6      3 2 14.46200 18.65500  6 Map Frame

> [1] 1241

length(unique(roads$street)) > [1] 528 The correspondence between these 528 “streets” and streets in the real world is not one-to-one. Excluding the 50 “streets” used to draw the map’s frame, the remaining 478 “streets” actually describe 206 real world roads (e.g., Oxford Street, Regent Street). This discrepancy emerges because real world streets are approximated using straight line segments. In fact 40% of the “real world” roads are composed of multiple “street” segments: for example, Oxford Street consists of 26 line segments and Broad Street consists of 6. # Map Border "Streets" # top <- c(1:12, 14) right <- c(37, 62, 74, 142, 147, 205, 240, 248, 280, 360, 405, 419, 465) bottom <- c(483, seq(487, 495, 2), 498, 500, seq(503, 519, 2)) left <- c(31, 79, 114, 285, 348, 397, 469) border <- sort(c(bottom, left, top, right)) length(border) > [1] 50 ## Road names The primary source for road names is Snow’s map (a high resolution version is available here. While great effort was made to correctly record and cross-reference names, there may still be errors. Error reports and suggestions for amendments are welcome. Some roads on the map do not have a name. In those cases, I attach unique labels like “Unknown-C”. Some names appear multiple times even though they lie at different locations. For these, I use Roman numerals to distinguish them (e.g., “King Street (I)” and “King Street (II)”).1 ## Queen Street (I) and Marlborough Mews There is one apparent coding error in Dodson and Tobler’s road data. Queen Street (I) extends too far: the water pump #5 is clearly located on Marlborough Mews (see map, cited above) but ends up on Queen Street (I). I amend this by moving the end point of Queen Street (I) westward so that the street only runs in a north-south direction. I do so by reassigning the segment that runs east-west to be part of Marlborough Mews. snow.streets <- HistData::Snow.streets snow.streets$id <- seq_len(nrow(snow.streets))

# Data frame of road names
stringsAsFactors = FALSE)

roads[is.na(roads$name), "name"] <- "Map Frame" roads[roads$id == 277, "street"] <- 116
roads[roads$id == 277, "name"] <- "Marlborough Mews" roads[roads$id == 277, c("x", "y")] <- roads[roads$id == 276, c("x", "y")] roads[roads$name == "Queen Street (I)", "n"] <- 4
roads[roads$name == "Marlborough Mews", "n"] <- 3 roads <- roads[order(roads$id), ]

## Finding roads by name, “street” number, or segment ID.

To help locate and visualize streets and road segments (including the map frame segments), you can use streetNameLocator(), streetNumberLocator(), or segmentLocator().

Note that streetNameLocator() uses the names from the roads data set and tries to corrects for case and for extra spaces: streetNameLocator("Oxford Street") and streetNameLocator("oxford street").

segmentLocator() provides more granular analysis. It uses individual road segments as the unit of observation.

There are 206 “valid” road names; 207, if we include “Map Frame”:

2   Air Street                         Margaret Court
3   Albany Street                      Margaret Street
4   Albemarle Street                   Market Court
5   Allens Court                       Market Place
6   Angel Court                        Market Row
7   Archer Street                      Market Street (I)
8   Argyll Place                       Market Street (II)
9   Argyll Street                      Marlborough Court
10  Arundel Place                      Marlborough Mews
11  Arundel Street                     Marlborough Row
12  Batemans Buildings                 Marshall Street
13  Beak Street                        Marylebone Street
14  Bentinck Street                    Masons Arms Yard
15  Berners Street                     Meards Court/Street
16  Berwick Street                     Mill Street
17  Black Lion Court                   Nags Head Yard
18  Blenheim Mews                      Naylors Yard
19  Blenheim Street                    New Bond Street
20  Boyle Street                       New Burlington Mews
21  Brewer Street                      New Burlington Street
22  Bridle Street                      New Street
23  Broad Street                       New Street/Husband Street
24  Bruton Street                      Newman Street
25  Bull Yard                          Noel Street
27  Burlington Gardens                 North Coventry Street
28  Cambridge Street                   Old Burlington Mews
29  Carlisle Street                    Old Burlington Street
30  Carnaby Court                      Old Compton Street
31  Carnaby Street                     Orchard Place
32  Castle Street East                 Oxendon Street
33  Catherine Wheel Yard               Oxford Street
34  Chapel Place                       Panton Street
35  Charles Street                     Perrys Place
36  Church Street                      Peter Street
37  Clifford Street                    Pews Place
38  Coach & Horses Yard                Phoenix Yard
40  Conduit Street                     Plough Yard
41  Cork Mews                          Poland Street
42  Cork Street                        Pollen Street
43  Coventry Street                    Portland Mews
44  Cross Street                       Portland Street
45  Crown Court                        Princes Street (I)
46  Dean Street                        Princes Street (II)
47  Dover Street                       Princes Street (III)
48  Duck Lane/Ham Square               Princes Street/Hanover Square
49  Dufours Place                      Pulteney Court (I)
50  Edward Street                      Pulteney Court (II)
51  Falconberg Court                   Queen Street (I)
52  Falconberg Mews                    Queen Street (II)
53  Fouberts Place                     Queen Street (III)
54  Francis Street                     Queens Head Court
55  Frith Street                       Rathbone Place
56  George Court (I)                   Regent Street
57  George Court (II)                  Regents Quadrant
58  George Place (?)                   Richmond Buildings/Mews
59  George Street                      Richmond Street
60  George Yard                        Rupert Street
61  Glasshouse Street                  Sackville Street
62  Golden Place                       Saville Row
63  Golden Square                      Sherrard Street
64  Grafton Street                     Ship Yard
65  Great Castle Street                Sidney Alley
66  Great Chapel Street                Silver Street
67  Great Crown Court                  Smiths Court/Yard
68  Great Marlborough Street           Soho Square
69  Great Pulteney Street              South Row
70  Great Windmill Street              St Anns Court
71  Greek Street                       St Anns Place
72  Green Dragon Yard                  St James Workhouse
73  Greens Court                       St James's Market
74  Ham Yard                           Sutton Street
75  Hanover Street                     Swallow Place
76  Hanway Street                      Swallow Street
77  Haymarket                          Tent Court
78  Heddon Court                       Tichborne Street
79  Heddon Street                      Titchfield Street
80  Hollen Street                      Turks Head Yard
81  Hopkins Street                     Tyler Court
82  Jermyn Street                      Tyler Street
83  John Street                        Tylers Court
84  Kemps Court                        Unknown-A1
85  King Street (I)                    Unknown-A2
86  King Street (II)                   Unknown-B
87  Kings Arms Yard                    Unknown-C
88  Leicester Street (I)               Upper James Street
89  Leicester Street (II)              Upper John Street
90  Lisle Street                       Upper Rupert Street
91  Little Argyll Street               Vigo Street
92  Little Chapel Street               Vine Street
93  Little Crown Court                 Walkers Court
94  Little Dean Street                 Wardour Mews
95  Little Marlborough Street          Wardour Street
96  Little Pulteney Street             Warwick Street
97  Little Windmill Street             Wellington Mews
98  Lower James Street                 Wells Street
99  Lower John Street                  West Street
100 Lowndes Court                      Whitcomb Court
101 Macclesfield Street                White Bear Yard
102 Macclesfield Street/Gerrard Street William and Mary Yard