Hello all, im quite new to all this Rstudio. but im trying to make a choropleth map of Denmark. ive got the map to show and work from a .rds file from gadm.org. but when i have to fill each polygon with other data (csv), i fall short and have no idea how to continue.
library(sp)
DK <- readRDS("dk2.rds")
library(tibble)
library(dplyr)
library(ggplot2)
##here the map is showing and everything is fine
ggplot(data = DK, aes(x=long, y=lat, group=group)) +
geom_polygon(fill="white", color="blue") +
coord_map()
##now trying to add the csv file
DKtal <- read.csv("DKtal2.csv")
##merging the two files
final_map <- merge(DK, DKtal, by = "NAME_2")
##plotting the new map with the fill set at "tal" which should assign a value to some of the regions in denmark. but nothing happens
ggplot(data = final_map, aes(x=long, y=lat, group=group)) +
geom_polygon(color="white", fill=tal) +
coord_map()
##all it gives me is this message
##Regions defined for each Polygons
##Error in layer(data = data, mapping = mapping, stat = stat, geom = GeomPolygon, :
## object 'tal' not found
So all in all I'm having problems with merging the two datasets correct i think.
any body who has an idea on what to do here?
When you work with data from gadm.org, you are downloading rds file that contains sf or sp object.
I think you need to convert also the data you read from csv to the corresponding format (sf or sp) and work with sf to merge the data.
Also, Could you ask this with a minimal REPRoducible EXample (reprex)? A reprex makes it much easier for others to understand your issue and figure out how to help.
I'd strongly recommend that you look into the sf package if you are going to be working with spatial data in R. It is quite a bit easier to work with than the previous standard spatial package, sp. In fact there was recently a great series of blogposts about making maps with sf and ggplot2: Drawing beautiful maps programmatically with R, sf and ggplot2 — Part 1: Basics
As to your specific question about merging non-spatial data with spatial data, the sf package allows you to use (nearly) all the dplyr functions on spatial objects as you would on any R data frame. So, you can use left_join() to merge data from a non-spatial data frame (like from your CSV) with an sf object, given that they have a column in common to join on.
Below, I grab the Denmark spatial data that you reference and then create a subset and remove the the spatial data from it to create a standard data frame (similar to what you might have in your CSV). Then I join that data frame with the sf object and plot it.
library(tidyverse)
library(sf)
#> Linking to GEOS 3.5.1, GDAL 2.1.3, PROJ 4.9.2
# read sf file
dk <- read_rds(gzcon(url("https://biogeo.ucdavis.edu/data/gadm3.6/Rsf/gadm36_DNK_2_sf.rds")))
# make sf subet
dk_a <- select(dk, 1:3, 7)
# make non spatial subset
dk_b <- dk %>%
select(4:7) %>%
st_set_geometry(NULL) %>%
mutate(my_rate = runif(99)) # make up some data to plot
# join spatial and non spatial
dk_merged <- left_join(dk_a, dk_b, by = "NAME_2")
# plot
ggplot(data = dk_merged) +
geom_sf(aes(fill = my_rate))
If your question's been answered (even by you!), would you mind choosing a solution? It helps other people see which questions still need help, or find solutions if they have similar problems. Here’s how to do it:
to merge the data.