Mapping coordinates to the world map and labeling them - r

Question

I have a dataframe with three columns: city_name, longitude, latitude. Using ggplot I am attempting to visualize the data using longitude and latitude as coordinates, which represent the given city. I also want to label each point with the city name. Unfortunately the scale isn't quite right, so the points are mapped in the right location.
Example data for dataframe:
city_name <- c("Berlin", "Brussels", "Paris")
longitude <- c("13.405", "4.3517", "2.3522")
latitude <- c("52.52", "50.8503", "48.8566")
df <- data.frame(city_name, longitude, latitude)
I am using ggplot2.
mapWorld <- borders("world", colour="gray50", fill="gray50") # create a layer of borders
ggplot(df, aes(x= longitude, y= latitude, label=Name))+
geom_point() +geom_text(aes(label=city_name),hjust=0, vjust=0) + mapWorld
Current result:
https://imgur.com/K3RvqTm
Expected result would be mapping the coordinates to their correct location.
Thank you all in advance!

Answer 1

The issue seems to stem from the format of your latitude and longitude data. Instead of quoting each coordinate, just refer to them without quotes.
I also recommend leaflet for a wider array of mapping functionality. The code below worked for me:
longitude <- c(13.405, 4.3517, 2.3522)
latitude <- c(52.52, 50.8503, 48.8566)
df <- data.frame(city_name, longitude, latitude)
library(leaflet)
df$longitude<-as.numeric(df$longitude)
df$latitude<-as.numeric(df$latitude)
leaflet() %>%
addTiles()%>%
addMarkers(data=df,lng=~longitude,lat=~latitude) %>%
setView(10,50,zoom=4)

Answer 2

On top of the solution already provided, you might find it helpful to look into the sf package which, in my opinion, makes spatial data much more pleasant to work with. For example you can do:
library(ggrepel)
library(sf)
library(ggplot2)
mapWorld <- borders("world", colour="gray50", fill="gray50") # create a layer of borders
# define data frame ensuring lat and lon are numeric vectors
df <- data.frame(city_name = c("Berlin", "Brussels", "Paris"),
longitude = c(13.405, 4.3517, 2.3522),
latitude = c(52.52, 50.8503, 48.8566))
# convert into an sf object, letting it know the columns we want to use for X and Y
# setting crs = 4326 for lon/lat data and remove = F to stop those columns from being dropped
df_sf <- st_as_sf(df, coords=c('longitude', 'latitude'), crs = 4326, remove = F)
# it plays nicely with ggplot via the 'geom_sf' geom
ggplot(df_sf)+
mapWorld +
geom_sf() +
geom_text_repel(aes(x=longitude, y=latitude,label=city_name))
You'll notice sf objects come with their own 'geometry' column which is recognised and plays nicely with ggplot. One thing to note is be careful with your layer ordering - by adding mapWorld to your ggplot as the last layer, it will appear at the very top of the plot and may cover your points!