Shapefile and location coordinates don't overlap each other

Question

I am trying to overlay a map of country with pointers on specific locations. For this I first downloaded the boundary of country and then the lat/lon values of the points I want to plot

library(rgeoboundaries)
boundary <- geoboundaries("Mongolia")

library(MODIStools)
points <- mt_sites() %>%
  filter(country == "Mongolia")

Then I tried to plot them together using ggplot2 but they dont overlay on each other.

library(ggplot2)
ggplot() +
  geom_sf(data = boundary) +
  geom_point(data = points,
             aes(x = latitude,
                 y = longitude))

Answer 1

Your points is a data.frame not a SpatialPointsDataFrame. So, first I have converted the data.frame to SpatialPointsDataFrame using coordinates(points) <- ~longitude + latitude. Then I have assigned it a crs (+proj=longlat +datum=WGS84 +no_defs). Then I have converted the sp object to sf object using st_as_sf and then I have plotted it like

library(rgeoboundaries)
library(raster)
library(tidyverse)
library(sf)
library(MODISTools)

boundary <- geoboundaries("Mongolia")

points <- mt_sites() %>%
  filter(country == "Mongolia")

#Check the coordinate reference of points and boundary
crs(points)
#> [1] NA
crs(boundary)
#> CRS arguments: +proj=longlat +datum=WGS84 +no_defs 

#See the class of the points
class(points)
#> [1] "data.frame"

#Convert the data.frame to SpatialPointsDataFrame
coordinates(points) <- ~longitude + latitude

#Assign the crs to points SpatialPointsDataFrame
crs(points) <- crs(boundary)

#Convert sp object to sf object
points_sf <- st_as_sf(points)

#Plot the results
ggplot() +
  geom_sf(data = boundary) +
  geom_sf(data = points_sf)