plot_fd_map(df, lon_col, lat_col, value_col)

plot_fd_map <- function(df, lon_col = "lon", lat_col = "lat", value_col,
                        palette = "viridis", point_size = 0.8) {
  if (!requireNamespace("rnaturalearth", quietly = TRUE))
    install.packages("rnaturalearth")
  library(ggplot2); library(rnaturalearth)
  
  world <- ne_countries(scale = "medium", returnclass = "sf")
  
  ggplot() +
    geom_sf(data = world, fill = "#f5f5f0", colour = "#cccccc", linewidth = 0.2) +
    geom_point(data = df,
               aes(.data[[lon_col]], .data[[lat_col]],
                   colour = .data[[value_col]]),
               size = point_size, alpha = 0.7) +
    scale_colour_viridis_c(option = palette, name = value_col) +
    coord_sf(expand = FALSE) +
    theme_minimal() +
    theme(axis.text = element_blank(), axis.ticks = element_blank(),
          panel.grid = element_line(colour = "#eeeeee"))
}