CREATE TABLE table_21378 ("Official Name" TEXT, "Status" TEXT, "Area km 2" TEXT, "Population" FLOAT, "Census Ranking" TEXT)

What is Petersville's census ranking?
SELECT "Census Ranking" FROM table_21378 WHERE "Official Name" = 'Petersville'
SELECT "Census Ranking" FROM "table_21378" WHERE "Official Name" = 'Petersville'