Embed Size (px)
Citation preview
$+
$+
$+
$+$+
$+
$+
$+ $+
$+$+
$+
$+ #
#
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GFGF
GF
GFGF
GFGF
GFGF
GFGFGFGFGFGF
GFGF
GF
GF
GF
GF
GF
GFGFGF
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GFGF
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GFGFGFGFGF
GF
GF
GF
GF
GF
GF
GFGF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GF
GFGF
GF
GF
GFGF
GFGF
GFGF
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GFGF
GF
GFGF
GF
GF
GF
GF
GF
GFGF
GF
GF
GFGF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GFGF
GF
GFGF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GFGF
GF
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GF
GFGF
GF
GF
GF
GF
GF
GFGF
GF
GFGF
GFGF
GFGF
GF
GFGF
GF
GFGFGFGF
GFGF
GF $+
$+
$+
$+ $+
$+
$+
$+ $+
$+ $+
$+
$+
$+
$+
$+$+
$+
$+
$+ $+
$+$+
$+
$+
$+
$+
$+$+
$+
$+
$+
$+$+
$+
The 1854 Broad Street Cholera Outbreak:1
2
3
4
5
6
A Modern Recreation ofHistoric Spatial Analysis
. John Snow's work in identifying the source of the 1854 Broad StreetCholera Outbreak in London (geographic context in Map 6) represents anearly application of spatial analysis that predates computer aided analysis.This map is a recreation of Snow's analysis using modern statisticaltechniques on Snow's original data, represented by Map 3.. The first stage in this analysis involved creating Thiessen Polygons (Map1). Each of these polygons represents the closest water pump within the areaof the study. Next, each death is allocated to the pump by it's location relativeto the Thiessen polygons. This was the extent of Snow's original research,which led to the disabling of the Broad Street Pump, the pump associatedwith the most deaths.. The next map (Map 2) shows the mean center (unweighted in purple,weighted in green) of the spatial distribution of deaths in the study area. Therelationship between these two points forms a theoretical line pointingtowards the densest area of the outbreak. The orange circle represents thestandard distance of deaths from the weighted mean center, or one standarddeviation of the distance from the weighted center of death locations, whichsupports Snow's initial hypothesis that the Broad Street Pump was the causeof the outbreak.. Map 4 depicts an Inverse Distance Weighted Interpolation of deaths bylocation within the study area. The gradient from yellow to red represents thelikelihood that a given cell has an influence on the spatial position of theinput data set, in this case, the death addresses data from Snow's originalanalysis. Water pumps falling in red areas are more likely to be spatiallyrelated to the location (weighted by the number) of deaths in the study area.Again, the Broad Street Pump appears to be in the center of this data set.
The final map, Map 5, shows a Hot Spot Analysis of Snow's data. The first step in this analysisinvolved using spatial autocorrelation to find out how the data related to itself in distance,looking at te distance from each location and comparing it to all of the other points of data todetermine how the data was clustered. Most data appeared to be clustered in areas ~110 meters inradius, with a sharp decline at ~120 meters. Using this information, Hot Spot Analysis looked atthe clusters of data to determine the statistiacal likeliness that any given cell was a Hot Spot, orrelated to the spatial distribution of the input data set. The Hot Spot Analysis tool also includesCold Spots, or locations that are statistically unlikely to be the source or a factor in the spatialdistribution of the input data. In this visualization Hot Spots are represented in red, while ColdSpots are represented in blue; areas with a low statistical likeliness to effect the spatialdistribution of the input data are depicted in yellow. This final level of analysis also pointed tothe Broad Street Pump as being the source of the 1854 Cholera Outbreak, further supportingSnow's historic hypothesis.
$+43 Broadwick Street$+1 Great Titchfield Street$+10 Ramillies Place$+2 Berners Street$+1 Newman Street$+1 Carnaby Street$+11 Warwick Street$+9 Vigo Street
$+ 20 A4$+ 52 Rupert Street$+ 54 Dean Street$+ 36 Bridle LaneGFCholera Deaths
#Weighted Spatial Mean Center# Spatial Mean Center
Standard Distance
7.83828
1
Map 4:IDW
Z-Scores
3.47303
-2.21557
Map 5:Hot SpotZ- Scores
Map created by Theodore Ahlvin for EcoGeo Consulting, 11/29/2014 Data Sources: WWU 2014, ESRI 2014 Projections: WGS 1984, UTM Zone 30N
¯ 0 100 200 300 40050Meters
