Both mean "local" but I'm not sure of the difference. I've heard different views. Is it
- Ντόπιος is for people and products (ψηφοφόροι, είσαι ντόπιος/α;, τυριά) and τοπικός is everything else (βιβλιοθήκες, εφημερίδες, όδοι).
- It's the point of view: if you are in the area referred to you use ντόπιος, if you are referring to different place to where you are, you use τοπικός.