Necessity is a synonym of Need. 
you are likely to find Closet in/at/on School. you are likely to find Box in/at/on Closet. Box is related to Ballot. Ballot is related to Butterfly. 
Necessity <--Synonym--> Need 
School <--AtLocation-- Closet <--AtLocation-- Box <--RelatedTo--> Ballot <--RelatedTo--> Butterfly 