How to add geospatial connections to ggplot map?

Question

Using this as a reference, I'm trying to build a map of the bottom forty-eighth and add layers to visualize the flow between states.

library(ggplot2)
library(maps)
library(geosphere) # to inter-polate a given pair of (lat,long) on the globe

# load map data for the US
all_states <- map_data("state")

# plot state map
p <- ggplot() + geom_polygon( data=all_states, 
                       aes(x=long, y=lat, group = group),
                       colour="white", fill="grey10" )

# sample origin - destination lat,long pairs
geo <- structure(list(orig_lat = c(36.17, 36.17, 36.17), 
orig_lon = c(-119.7462, -119.7462, -119.7462), dest_lat = c(33.7712, 36.17, 39.0646), 
    dest_lon = c(-111.3877, -119.7462, -105.3272)), .Names = c("orig_lat", 
"orig_lon", "dest_lat", "dest_lon"), row.names = c(NA, 3L), class = "data.frame")

#> geo
#  orig_lat  orig_lon dest_lat  dest_lon
#1    36.17 -119.7462  33.7712 -111.3877
#2    36.17 -119.7462  36.1700 -119.7462
#3    36.17 -119.7462  39.0646 -105.3272

# list to hold a dataframe of interpolated points for each origin-destination pair
list_lines <- list()

# use the geosphere package gcIntermediate function to generate 50 interpolated  
# points for each origin-destination pair
for (i in 1:3) {
  inter <- as.data.frame(gcIntermediate(c(geo[i,]$orig_lon, geo[i,]$orig_lat), 
                                        c(geo[i,]$dest_lon, geo[i,]$dest_lat), 
                                        n=50, addStartEnd=TRUE))
  list_lines[i] <- list(inter)
  p <- p + geom_line( data = list_lines[[i]], aes(x = lon, y = lat), color = '#FFFFFF')
}
p

This is what I get when I try to print the plot

p
Error in eval(expr, envir, enclos) : object 'lon' not found

I tried debugging this and found that it works

p + geom_line( data = list_lines[[1]], aes(x = lon, y = lat), color = '#FFFFFF')

but adding another layer for the second element of the list violates it, but what, as far as I could get with my limited knowledge of both R and ggplot!

Answer 1

gcIntermediate returns different column names (since for i = 2 the source and target destinations are identical):

for (i in 1:3) {
  inter <- as.data.frame(gcIntermediate(c(geo[i,]$orig_lon, geo[i,]$orig_lat), 
                                        c(geo[i,]$dest_lon, geo[i,]$dest_lat), 
                                        n=50, addStartEnd=TRUE))
  print(head(inter, n=2))
}
     lon   lat
1 -119.7 36.17
2 -119.6 36.13
      V1    V2
1 -119.7 36.17
2 -119.7 36.17
     lon   lat
1 -119.7 36.17
2 -119.5 36.24

The following lines should work:

for (i in 1:3) {
  inter <- as.data.frame(gcIntermediate(c(geo[i,]$orig_lon, geo[i,]$orig_lat), 
                                        c(geo[i,]$dest_lon, geo[i,]$dest_lat), 
                                        n=50, addStartEnd=TRUE))
  names(inter) <- c("lon", "lat")
  p <- p + geom_line(data=inter, aes(x=lon, y=lat), color='#FFFFFF')
}

Answer 2

, , : long script lon . , , , .

, geom . geom_line color .

Answer 3

, ggplot2. R ggplot2, .

p + 
  geom_segment(data = geo, aes(x = orig_lon,    y = orig_lat, 
                               xend = dest_lon, yend = dest_lat,
                               color="#FFFFFF")) +  coord_equal()