When buffalo narrows is the name how many measurements of population density per kilometer squared are there?
CREATE TABLE "northern_villages" (
  "name" text,
  "population_2011" real,
  "population_2006" real,
  "change_pct" text,
  "land_area_km" text,
  "population_density_per_km" text
);
SELECT COUNT("population_density_per_km") FROM "northern_villages" WHERE "name"='Buffalo Narrows';