How many locations had a density (pop/km²) of 91.8 in the 2011 census?
CREATE TABLE "references" (
  "name" text,
  "2011_census" real,
  "2006_census" real,
  "pct_change" text,
  "land_area_km" text,
  "density_pop_km" text,
  "population_rank" real
);
SELECT COUNT("2011_census") FROM "references" WHERE "density_pop_km"='91.8';