Country is related to Desert. you are likely to find Sand in/at/on Desert. you are likely to find Sand in/at/on Earth. 
you are likely to find Desk in/at/on Library. Library is related to Rent. Rent is related to Room. 
Country <--RelatedTo--> Desert <--AtLocation-- Sand --AtLocation--> Earth 
Desk --AtLocation--> Library <--RelatedTo--> Rent <--RelatedTo--> Room 