# Roads

#### lindbrook

#### 2019-03-08

## 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.

## Roads data

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”.

    head(roads)
    >   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

    nrow(roads)
    > [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
    road.data <- read.csv("~/Documents/Data IV/Snow/road3b.csv",
      stringsAsFactors = FALSE)

    roads <- merge(snow.streets, road.data, by = "street", all.x = TRUE)
    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.

## List of road names

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

    1   Adam and Eve Court                 Maidenhead Court
    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
    26  Burlington Arcade                  Norris's Place
    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
    39  Cock Court                         Picadilly
    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
    103 Maddox Street                      Winsley Street

## Coordinate unit

The original map is 14.5 x 15.5 inches with a stated nominal scale of 30 inches per mile.

Dodson and Tobler write that “The scale of the source map is approx. 1:2000. Coordinate units are meters.” By my estimate, one unit on the map is approximately 177 feet or 54 meters per unit.2

1. Streets with the same name were not an unusual occurrence. See Judith Flanders. 2012. The Victorian City: everyday life in Dickens’ London. New York: St. Martin’s Press, 57-58.↩

2. According to Dodson and Tobler’s data, the length of Carnaby Street from its intersection with Great Marlborough to its intersection with Silver Street is 2.61 units. According to Google Maps, the approximate analog of that segment is the distance along parts of Great Marlborough Street and Carnaby Street between 19-21 Great Marlborough Street and 43 Carnaby Street (at Ganton Street): 463 ft. This translates into approximately 177 feet/unit or 54 meters/unit.↩