In what urban area is the 2011 population 21561? 
CREATE TABLE "see_also" (
  "rank_2011" real,
  "change_since_2006" text,
  "urban_area" text,
  "county" text,
  "population_2011" real,
  "increase_since_2006" text
);
SELECT "urban_area" FROM "see_also" WHERE "population_2011"=21561;