Customizing Choropleth Map

I am trying to make a Choropleth map with several countries from Asia. Below you can see the code and countries.

 library(ggplot2)
  library(maps)
  
  datar <- data.frame(GEO = c("AR","AZ","TR","GA","IR"), 
                      Value = c(0.2560,0.023,0.0120,0.158,0.0025),
                      search_countries = factor(c("Armenia","Azerbaijan","Turkey","Georgia","Iran")),
                      countries = c("Armenia","Azerbaijan","Turkey","Georgia","Iran")
  )
  
  mapa <- map_data('world', region = datar$search_countries)
  
  ggplot() + 
    geom_map(data = mapa, map = mapa, aes(x = long, y = lat,map_id = region)) +
    geom_map(data = datar, map = mapa, aes(fill = Value, map_id = countries), color ='black', size = .25) +
    coord_map() 

Now I want to customize this map. Namely, on the map I want to see the names of the countries and also I want to see lakes.

So can anybody help me how to solve this problem?

You will need to get a hold of more detailed maps, including specific maps of lakes. You can get high definition maps from the rnaturalearth package.

library(ggplot2)
library(rnaturalearth)
library(sf)

url <- paste0("https://www.naturalearthdata.com/",
              "http//www.naturalearthdata.com/download/10m/physical/",
              "ne_10m_lakes.zip")

path <- tempdir()
download.file(url, paste0(path, "/lakes.zip"))
unzip(paste0(path, "/lakes.zip"))
lakes <- read_sf("ne_10m_lakes.shp")

We can combine detailed outlines of countries and lakes to your own data like so:

datar <- data.frame(GEO = c("AR", "AZ", "TR", "GA", "IR"), 
                    Value = c(0.2560, 0.023, 0.0120, 0.158, 0.0025),
                    search_countries = factor(c("Armenia", "Azerbaijan",
                                                "Turkey", "Georgia", "Iran")),
                    countries = c("Armenia", "Azerbaijan", "Turkey", "Georgia",
                                  "Iran"))

datar$geometry <- ne_countries(scale = 10, 
                               country = datar$countries, 
                               returnclass = "sf")$geometry

datar$centroid <- st_centroid(datar$geometry)

Then the plotting code is pretty straightforward

ggplot(datar) + 
  geom_sf(aes(geometry = geometry, fill = Value)) +
  geom_sf(data = lakes, color = NA, fill = "white") +
  geom_sf_text(aes(geometry = centroid, label = countries)) +
  coord_sf(xlim = st_bbox(datar$geometry)[c(1, 3)],
           ylim = st_bbox(datar$geometry)[c(2, 4)]) +
  theme_classic(base_size = 20) +
  theme(panel.border = element_rect(fill = NA)) +
  scale_fill_gradient(low = "#d0d8c8", high = "#ffd8d0")