What is the census rating of the city with the official name "Plaster Rock"?
SELECT T1.Census_Ranking FROM city AS T1 JOIN farm_competition AS T2 ON T1.City_ID   =   T2.Host_city_ID where T1.Official_Name  =  "Plaster Rock"
census rating refers to Census_Ranking; city with the official name \"Plaster Rock\" refers to T1.Official_Name = \"Plaster Rock\"; join condition is T1.City_ID = T2.Host_city_ID;