The term "Gutter Line" in the context of Ragnarok GRF download seems to relate to a custom or specific GRF file or collection aimed at enhancing or modifying the game's map or graphical assets. The term "gutter" might imply a focus on edges or borders within the game's visual presentation, possibly referring to a modification that alters or enhances map textures, specifically line or edge details.
If you want to view the Gutter Line map in a map editor (like BrowEdit ): ragnarok gutter line grf download