MTA (version 0.1.2)

sdev: Spatial Deviation

Description

This function computes the deviation between regional ratios and local ratios. Local ratios are defined either by a contiguity order or by a distance measure between regions. Each elementary unit value will be compared to the value of its neighborhood.

Usage

sdev(x, var1, var2, type = "rel", spdf, order = NULL, dist = NULL,
  mat = NULL, spdfid = NULL, xid = NULL)

Arguments

x

a data frame.

var1

name of the numerator variable in x.

var2

name of the denominator variable in x.

type

type of deviation; "rel" for relative deviation, "abs" for absolute deviation (see Details).

spdf

a SpatialPolygonsDataFrame that matches x data frame.

order

contiguity order.

dist

distance threshold defining the contiguity. The cartesian distance between units centroids is used by default (see gDistance); use mat to apply different metrics.

mat

a distance matrix (road distance, travel time...) between x units. Row and column names must fit xid identifiers. (optional)

spdfid

identifier field in spdf, default to the first column of the spdf data frame. (optional)

xid

identifier field in x, default to the first column of x. (optional)

Value

A vector is returned.

Details

The relative spatial deviation is the ratio between var1/var2 and var1/var2 in the specified neighborhoud. Values greater than 100 indicate that the unit ratio is greater than the ratio in its neighborhoud. Values lower than 100 indicate that the unit ratio is lower than the ratio in its neighborhoud. The absolute spatial deviation is the amount of numerator that could be moved to obtain the same ratio in all units of its neighborhoud.

Examples

# NOT RUN {
# load data
data("GrandParisMetropole")
# compute absolute spatial deviation in a neighborhood defined by a contiguity 
# order of 2.
com$sdevabs <- sdev(x = com, var1 = "INC", var2 = "TH", 
                          type = "abs", spdf = com.spdf, order = 2)

# compute relative spatial deviation in a neighborhood defined within a distance 
# of 5km between communes' centroids 
com$sdevrel <- sdev(x = com, var1 = "INC", var2 = "TH", type = "rel", 
                          spdf = com.spdf, dist = 5000)

# compute absolute spatial deviation in a neighborhood defined within a road 
# travel time of 10 minutes by car
com$scardevabs <- sdev(x = com, var1 = "INC", var2 = "TH", type = "abs", 
                             spdf = com.spdf, dist = 10, mat = cardist)
# compute relative spatial deviation in a neighborhood defined within a road 
# travel time of 10 minutes by car
com$scardevrel <- sdev(x = com, var1 = "INC", var2 = "TH", type = "rel", 
                             spdf = com.spdf, dist = 10, mat = cardist)

# map deviations
if(require('cartography')){
  library(sp)
  # set graphical parameters
  par(mar = c(0,0,1.2,0))
  # set breaks
  bks <- c(min(com$scardevrel),50,75,100,125,150,max(com$scardevrel))
  bks <- sort(bks)
  # set colot palette
  cols <- carto.pal(pal1 = "blue.pal", n1 = 3,
                    pal2 = "wine.pal", n2 = 3)
  # plot a choropleth map of the relative spatial deviation
  choroLayer(spdf = com.spdf, df = com, var = "scardevrel",
             legend.pos = "topleft",
             legend.title.txt = "Relative Deviation",
             breaks = bks, border = NA,
             col = cols)
  # add symbols proportional to the absolute spatial deviation
  com$sign <- ifelse(test = com$scardevabs<0, yes = "negative", no = "positive")
  propSymbolsTypoLayer(spdf = com.spdf, df = com, var = "scardevabs",var2 = "sign",
                       legend.var.pos = "left",legend.values.rnd = -2, 
                       legend.var2.values.order = c("positive", "negative"),
                       legend.var.title.txt = "Absolute Deviation",
                       col = c("#ff000050","#0000ff50"),legend.var2.pos = "n",
                       legend.var.style = "e", inches = 0.2)
  # add a layout
  layoutLayer(title = "Spatial Deviation (neighborhoud: 10 minutes by car)",
              sources = "GEOFLA<U+00AE> 2015 v2.1, impots.gouv.fr", north = TRUE,
              author = "MTA")
}
# }