How to fill a map from a shapefile using its own attributes table in R?

Question

I see some people using R to fill maps from shapefiles, e.g. here. With my R knowledge, I only read the shapefile and plot it.

With QGIS I added an extra column to the attribute table called "OCCURENCE". This column is a year when a specific event occurred. I'd like to fill each country according to the year of occurence using a color scale, leaving the countries with no data without fill. The folder with the shapefiles is here. As example, I added some years to a few countries, and I like to obtain something like:

and a legend .

library(rgdal)
library(ggplot2)

World <- readOGR(dsn = "mundo", layer = "mundo")
class(World)

World2 <- fortify(World)
class(World2)

ggplot() + 
  geom_polygon(data = World2, aes(x = long, y = lat, group = group),
               colour = "black", size = 0.5, fill = "white")

Any help??

What choropleth answers on SO were unhelpful so we know what research you did for this heavily asked question and can then not spin cycles suggesting things you already knew/did. — hrbrmstr, Dec 06 '17 at 03:13
In a simple way, you can use the `sf` package. `mydata <- st_read(dsn = ".", layer = "mundo"); ggplot() + geom_sf(data = mydata, aes(fill = OCCURENCE))` — jazzurro, Dec 06 '17 at 03:22

score 3 · Answer 1 · answered Dec 06 '17 at 10:41

The simple way, as @jazzurro said, is to work with sf package. But, you can achieve this with the method proposed by you adding a couple of steps.

You need to add an id field in SpatialPolygonsDataFrame and join these attributes with fortify() product. With this, you can fill polygons with any field:

library(rgdal)
library(ggplot2)

World <- readOGR(dsn = "mundo", layer = "mundo")
class(World)

World2 <- fortify(World)
class(World2)

World@data$id <- 0:(dim(World@data)[1]-1) # add id field

World2_join = plyr::join(x = World2,y = World@data, by="id") # join by id

ggplot() + 
  geom_polygon(data = World2_join, aes(x = long, y = lat, group = group, fill = OCCURENCE), # fill by OCCURENCE
               colour = "black", size = 0.5)

How to fill a map from a shapefile using its own attributes table in R?

1 Answers1