install.load::load_package("ie2miscdata", "USA.state.boundaries", "data.table", "ggplot2", "sf", "spatstat.geom")
# load needed packages using the load_package function from the install.load package (it is assumed that you have already installed these packages)


data(weather_results)
# load the weather_results data (containing the site information for USA weather stations)

data(state_boundaries_wgs84)
# load the state_boundaries_wgs84 data from USA.state.boundaries (for the USA map)


## Weather Results

weather_results_map <- copy(weather_results)
# copy the weather_results using data.table

setnames(weather_results_map, 3:4, c("lat", "lon"))
# set the names of columns 3 and 4 using data.table

weather_results_map_sf <- st_as_sf(weather_results_map, coords = c("lon", "lat"), crs = "+proj=longlat +datum=NAD83")
# set the initial projection to longlat using sf

weather_results_map_sf_projected <- st_transform(weather_results_map_sf, "+proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23 +lon_0=-96 +x_0=0 +y_0=0 +datum=NAD83 +units=m +no_defs +ellps=GRS80 +towgs84=0,0,0")
# transform the coordinates to match those of the USA_state_boundaries_map data from USA.state.boundaries.data (formerly in USA.state.boundaries)


## USA

USA <- state_boundaries_wgs84
# create the USA object with the same data as state_boundaries_wgs84

USA_projected <- st_transform(USA, "+proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23 +lon_0=-96 +x_0=0 +y_0=0 +datum=NAD83 +units=m +no_defs +ellps=GRS80 +towgs84=0,0,0")
# transform the coordinates to match those of the USA_state_boundaries_map data from USA.state.boundaries.data (formerly in USA.state.boundaries)


# As different methods using sf failed to subset the weather map points within the USA, the weather results geometry was subsetted so that spatstat.geom could be used to determine this information

weather_results_map_dt <- as.data.table(st_coordinates(weather_results_map_sf_projected))
# transform the coordinates only to a data.table

setnames(weather_results_map_dt, c("X", "Y"), c("lon", "lat"))
# set the names of columns X and Y using data.table


USA_owin <- spatstat.geom::as.owin(USA_projected)
# transform to Window


inside_USA <- which(spatstat.geom::inside.owin(weather_results_map_dt$lon, weather_results_map_dt$lat, USA_owin))
# determine which locations are within the borders of the USA (including Alaska, Hawai'i, Puerto Rico, and the U.S. Virgin Islands)
# Source 2


weather_results_keep <- weather_results[inside_USA, ]
# keep only the locations within the USA

weather_results_map_keep <- copy(weather_results_keep)
# create a data.table copy of the sites that are kept

setnames(weather_results_map_keep, 3:4, c("lat", "lon"))
# set the names of columns 3 and 4 using data.table

weather_results_map_keep_sf <- st_as_sf(weather_results_map_keep, coords = c("lon", "lat"), crs = "+proj=longlat +datum=WGS84 +ellps=WGS84")
# set the projection to longlat using sf

# plot the map using ggplot2
p <- ggplot() + geom_sf(data = USA, colour = "black", fill = "white")
p <- p + geom_sf(data = weather_results_map_keep_sf, colour = "#3591d1", size = 0.5)
p <- p + labs(x = "", y = "", title = "USA Engineering Weather Sites Map")
print(p)