Dense is a synonym of Tough. Tough is related to Gang. Nest is a type of Gang. Nest is related to Container. 
Urban is related to Feel. Burn is a type of Feel. Burn is related to Ash. 
Dense <--Synonym--> Tough <--RelatedTo--> Gang <--IsA-- Nest <--RelatedTo--> Container 
Urban <--RelatedTo--> Feel <--IsA-- Burn <--RelatedTo--> Ash 