Star Map - Buy

(Indefinite Article): Use "a" if you mean any star map in general or if you haven't picked a specific one yet.

"I decided to buy the star map we saw online". buy star map

The proper article depends on whether you are referring to a generic item or a specific, already-identified map: (Indefinite Article): Use "a" if you mean any

"I want to buy a star map for my anniversary". buy star map