CODEWITHSUNDEEP
rggplot2data-visualizationgeospatialr-sf
Miao Cai
Miao Cai

Reputation: 1014

Adding points to geom_sf shapes does not work when adding a projection

When I am trying to add points layer to a geom_sf() layer and a projection, the points seem to end up in one location in South Texas. Below is a minimal example of reproducing this issue.

library(sf)
library(ggplot2)
# devtools::install_github("hrbrmstr/albersusa")
library(albersusa)
crs_use = "+proj=laea +lat_0=30 +lon_0=-95"

d_points = data.frame(long = c(-110, -103, -84), 
                      lat  = c(45, 40, 41))

A = ggplot(data = usa_sf()) +
  geom_sf() + 
  geom_point(data = d_points, 
             aes(x = long, y = lat), 
             color = "red", size = 5) + 
  theme_minimal() + 
  ggtitle("(A) right point position, wrong projection")

B = ggplot(data = usa_sf()) +
  geom_sf() + 
  geom_point(data = d_points, 
             aes(x = long, y = lat), 
             color = "red", size = 5) + 
  coord_sf(crs = crs_use) + 
  theme_minimal() + 
  ggtitle("(B) right projection, wrong points using geom_point()")

C = ggplot() + 
  geom_sf(data = usa_sf()) + 
  geom_sf(data = st_as_sf(d_points,
                          coords = c("long", "lat"), crs = crs_use), 
          color = "red", size = 5) + 
  coord_sf(crs = crs_use) + 
  theme_minimal() + 
  ggtitle("(C) right projection, wrong points using geom_sf() points")

cowplot::plot_grid(A, B, C, nrow = 3)

enter image description here

I want to add a points layer to the US map with a custom projection. However, whenever I use a projection, the points that I specify become a weird location in Southeast Texas, which is not in my specified location.

Any suggestion on solving this issue is appreciated. Thank you!

Upvotes: 2

Views: 3355

Answers (1)

Jindra Lacko
Jindra Lacko

Reputation: 8749

You need to reproject your points as well; sf::st_transform() should do the job.

I don't have access to the {albersusa} package, so I am using {USABoundaries} to get a map of the lower 48, but that is not the point; the point is applying st_transform(crs = crs_use) to both your spatial objects before plotting.

library(sf)
library(ggplot2)
library(USAboundaries)

crs_use <- "+proj=laea +lat_0=30 +lon_0=-95"

usa_sf <- us_boundaries(type="state", resolution = "low") %>% 
  dplyr::filter(!state_abbr %in% c("PR", "AK", "HI")) %>% 
  st_transform(crs = crs_use)

d_points <- data.frame(long = c(-110, -103, -84), 
                      lat  = c(45, 40, 41)) %>% 
  st_as_sf(coords = c("long", "lat"), crs = 4326) %>% 
  st_transform(crs = crs_use)

ggplot(data = usa_sf) +
  geom_sf() + 
  geom_sf(data = d_points, 
             color = "red", size = 5) + 
  theme_minimal()

enter image description here

Upvotes: 6

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