pacman::p_load(sf,tmap,tidyverse)Hands-on_Ex08c
23 Analytical Mapping
23.2.1 Installing and loading packages
23.2.2 Importing data
NGA_wp <- read_rds("Data/NGA_wp.rds")23.3 Basic Choropleth Mapping
23.3.1 Visualising distribution of non-functional water point
p1 <- tm_shape(NGA_wp) +
tm_polygons(fill = "wp_functional",
fill.scale = tm_scale_intervals(
style = "equal",
n = 10,
values = "brewer.blues"),
fill.legend = tm_legend(
position = c("right", "bottom"))) +
tm_borders(lwd = 0.1,
fill_alpha = 1) +
tm_title("Distribution of functional water point by LGAs")
p2 <- tm_shape(NGA_wp) +
tm_polygons(fill = "total_wp",
fill.scale = tm_scale_intervals(
style = "equal",
n = 10,
values = "brewer.blues"),
fill.legend = tm_legend(
position = c("right", "bottom"))) +
tm_borders(lwd = 0.1,
fill_alpha = 1) +
tm_title("Distribution of total water point by LGAs")
tmap_arrange(p2, p1, nrow = 1)
23.4 Choropleth Map for Rates
23.4.1 Deriving Proportion of Functional Water Points and Non-Functional Water Points
NGA_wp <- NGA_wp %>%
mutate(pct_functional = wp_functional/total_wp) %>%
mutate(pct_nonfunctional = wp_nonfunctional/total_wp)23.4.2 Plotting map of rate
tm_shape(NGA_wp) +
tm_polygons(fill="pct_functional",
fill.scale = tm_scale_intervals(
style = "equal",
n = 10,
values = "brewer.blues"),
fill.legend = tm_legend(
position = c("right", "bottom"))) +
tm_borders(lwd = 0.1,
fill_alpha = 1) +
tm_title("Rate map of functional water point by LGAs")
23.5 Extreme Value Maps
23.5.1.1 Data Preparation
# Step 1: Exclude records with NA
NGA_wp <- NGA_wp %>%
drop_na()
# Step 2: Creating customised classification and extracting values
percent <- c(0,.01,.1,.5,.9,.99,1)
var <- NGA_wp["pct_functional"] %>%
st_set_geometry(NULL)
quantile(var[,1], percent) 0% 1% 10% 50% 90% 99% 100%
0.0000000 0.0000000 0.2169811 0.4791667 0.8611111 1.0000000 1.0000000 23.5.1.3 Creating the get.var function
get.var <- function(vname,df) {
v <- df[vname] %>%
st_set_geometry(NULL)
v <- unname(v[,1])
return(v)
}23.5.1.4 A percentile mapping function
percentmap <- function(vnam, df, legtitle=NA, mtitle="Percentile Map"){
percent <- c(0,.01,.1,.5,.9,.99,1)
var <- get.var(vnam, df)
bperc <- quantile(var, percent)
tm_shape(df) +
tm_polygons() +
tm_shape(df) +
tm_polygons(vnam,
title=legtitle,
breaks=bperc,
palette="Blues",
labels=c("< 1%", "1% - 10%", "10% - 50%", "50% - 90%", "90% - 99%", "> 99%")) +
tm_borders() +
tm_layout(main.title = mtitle,
title.position = c("right","bottom"))
}23.5.1.5 Test drive the percentile mapping function
percentmap("total_wp", NGA_wp)
23.5.2 Box map
ggplot(data = NGA_wp,
aes(x = "",
y = wp_nonfunctional)) +
geom_boxplot()
23.5.2.1 Creating the boxbreaks function
The code chunk below is an R function that creating break points for a box map.
arguments:
v: vector with observations
mult: multiplier for IQR (default 1.5)
returns:
- bb: vector with 7 break points compute quartile and fences
boxbreaks <- function(v,mult=1.5) {
qv <- unname(quantile(v))
iqr <- qv[4] - qv[2]
upfence <- qv[4] + mult * iqr
lofence <- qv[2] - mult * iqr
# initialize break points vector
bb <- vector(mode="numeric",length=7)
# logic for lower and upper fences
if (lofence < qv[1]) { # no lower outliers
bb[1] <- lofence
bb[2] <- floor(qv[1])
} else {
bb[2] <- lofence
bb[1] <- qv[1]
}
if (upfence > qv[5]) { # no upper outliers
bb[7] <- upfence
bb[6] <- ceiling(qv[5])
} else {
bb[6] <- upfence
bb[7] <- qv[5]
}
bb[3:5] <- qv[2:4]
return(bb)
}23.5.2.2 Creating the get.var function
The code chunk below is an R function to extract a variable as a vector out of an sf data frame.
arguments:
vname: variable name (as character, in quotes)
df: name of sf data frame
returns:
- v: vector with values (without a column name)
get.var <- function(vname,df) {
v <- df[vname] %>% st_set_geometry(NULL)
v <- unname(v[,1])
return(v)
}23.5.2.3 Test drive the newly created function
var <- get.var("wp_nonfunctional", NGA_wp)
boxbreaks(var)[1] -56.5 0.0 14.0 34.0 61.0 131.5 278.023.5.2.4 Boxmap function
boxmap <- function(vnam, df,
legtitle=NA,
mtitle="Box Map",
mult=1.2){
var <- get.var(vnam,df)
bb <- boxbreaks(var)
tm_shape(df) +
tm_polygons() +
tm_shape(df) +
tm_fill(vnam,title=legtitle,
breaks=bb,
palette="Blues",
labels = c("lower outlier",
"< 25%",
"25% - 50%",
"50% - 75%",
"> 75%",
"upper outlier")) +
tm_borders() +
tm_layout(main.title = mtitle,
main.title.size = 1.5,
legend.outside.position = "right",
title.position = c("right",
"bottom"))
}tmap_mode("plot")
boxmap("wp_nonfunctional", NGA_wp)