What is the land area of Switzerland with a population density fewer than 188 km²?
CREATE TABLE "ranking" (
  "country" text,
  "population_july_2005_est" real,
  "land_area_km" real,
  "pct_of_arable_land_2005_est" text,
  "arable_land_km" real,
  "population_density_pop_per_km" real
);
SELECT AVG("land_area_km") FROM "ranking" WHERE "country"='switzerland' AND "population_density_pop_per_km"<188;