How to add diagonal lines in NA value polygons using ggplot? - r

Question

I'm working to plot the consolidated Z-value deviations (for a series of factors) from the national average for Pakistan on a fortified SPDF. For the purposes of this question, my data is irrelevant. I could provide it if necessary.
I am using ggplot to create my output where the command and result look something like this:
ggplot() + geom_polygon(data = plot.pakmod_sumZ, aes(x = long, y = lat, group = group, fill = SumZ.Cat), color = "black", size = 0.25, na.rm = TRUE) + scale_fill_manual(name = "Deviations from National Average", labels = c("-7", "-6", "-5", "-4", "-3", "-2", "-1", "Positive"), values = c("darkorange4","brown", "orangered1","tomato1","darkorange3","orange","yellow", "greenyellow"), na.value = "Grey", guide = guide_legend(reverse = TRUE)) + coord_map() + labs(x = NULL, y = NULL) + scale_x_discrete(breaks = NULL) + scale_y_discrete(breaks = NULL) + theme_minimal()
Deviations from National Average
I am trying to figure out now if it's possible to add diagonal lines in the polygons which have missing values and are coloured grey. Can this be done using ggplot?

Answer 1

This is an example I took from here. I opted to use the horizontal error bar geom. Mind that this isn't the only way of doing this.
library(ggplot2)
library(sp)
library(rgdal)
library(rgeos)
# create a local directory for the data
localDir <- "R_GIS_data"
if (!file.exists(localDir)) {
dir.create(localDir)
}
# download and unzip the data
url <- "ftp://www.ecy.wa.gov/gis_a/inlandWaters/wria.zip"
file <- paste(localDir, basename(url), sep='/')
if (!file.exists(file)) {
download.file(url, file)
unzip(file,exdir=localDir)
}
# create a layer name for the shapefiles (text before file extension)
layerName <- "WRIA_poly"
# read data into a SpatialPolygonsDataFrame object
dataProjected <- readOGR(dsn=localDir, layer=layerName)
dataProjected#data$id <- rownames(dataProjected#data)
# create a data.frame from our spatial object
watershedPoints <- fortify(dataProjected)
# merge the "fortified" data with the data from our spatial object
watershedDF <- merge(watershedPoints, dataProjected#data, by = "id")
dataProjected#data$id <- rownames(dataProjected#data)
watershedPoints <- fortify(dataProjected)
watershedDF <- merge(watershedPoints, dataProjected#data, by = "id")
ggWatershed <- ggplot(data = watershedDF, aes(x=long, y=lat, group = group, fill = WRIA_NM)) +
geom_polygon() +
geom_path(color = "white") +
scale_fill_hue(l = 40) +
coord_equal() +
theme(legend.position = "none", title = element_blank())
# Adding coordinates to the data part of SPDF. `sd` is the variable of interest
# which is beign plotted here. Each line extends sd away from long coordinate
dataProjected#data$sd <- rnorm(nrow(xy), mean = 50000, sd = 10000)
xy <- coordinates(dataProjected)
dataProjected#data$long <- xy[, 1]
dataProjected#data$lat <- xy[, 2]
ggWatershed +
geom_errorbarh(data = dataProjected#data, aes(group = id, xmin = long - sd, xmax = long + sd))