Plot coordinates on map

An other alternative, is the plotGoogleMaps package which allows to plot in a navigator, allowing to zoom in and out etc. You can then make a screenshot of your picture to save it (though remember google maps are legally supposed to be used for the internet).

 library("plotGoogleMaps")
 lat <- c(-38.31, -35.50) #define our map's ylim
 lon <- c(40.96,37.50) #define our map's xlim

 # make your coordinates a data frame 
 coords <- as.data.frame(cbind(lon=lon,lat=lat))

 # make it a spatial object by defining its coordinates in a reference system
 coordinates(coords) <- ~lat+lon 

 # you also need a reference system, the following should be a fine default
 proj4string(coords) <- CRS("+init=epsg:4326")
 # Note: it is a short for: 
 CRS("+init=epsg:4326")
 > CRS arguments:
 >  +init=epsg:4326 +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0 

 # then just plot
 a <- plotGoogleMaps(coords)
 # here `a <-` avoids that you get flooded by the html version of what you plot 

And you get :

As an alternative to RgoogleMaps, you can also use the combination ggplot2 with ggmap.

With this code:

# loading the required packages
library(ggplot2)
library(ggmap)

# creating a sample data.frame with your lat/lon points
lon <- c(-38.31,-35.5)
lat <- c(40.96, 37.5)
df <- as.data.frame(cbind(lon,lat))

# getting the map
mapgilbert <- get_map(location = c(lon = mean(df$lon), lat = mean(df$lat)), zoom = 4,
                      maptype = "satellite", scale = 2)

# plotting the map with some points on it
ggmap(mapgilbert) +
  geom_point(data = df, aes(x = lon, y = lat, fill = "red", alpha = 0.8), size = 5, shape = 21) +
  guides(fill=FALSE, alpha=FALSE, size=FALSE)

you get this result:

Another option is using the leaflet package (as suggested here). Unlike Google Maps it does not require any API key.

install.packages(c("leaflet", "sp"))
library(sp)
library(leaflet)
df <- data.frame(longitude = runif(10, -97.365268, -97.356546), 
                 latitude = runif(10, 32.706071, 32.712210))

coordinates(df) <- ~longitude+latitude
leaflet(df) %>% addMarkers() %>% addTiles()