Table: country_density
Columns: country
population_july_2005_est
land_area_km
of_arable_land_2005_est
arable_land_km
population_density_pop_per_km

Question: What is the land area of Switzerland with a population density fewer than 188 km²?
SQL: SELECT AVG("land_area_km") FROM country_density WHERE "country" = 'switzerland' AND "population_density_pop_per_km" < 188