ABSTRACT Isoline extraction is influenced by numerical differences between grid cell neighbors. Due to varying neighborhood distances and directions of a traditional square grid cell across geographical space, numerical differences fail to precisely reflect the trends of terrain features. Alternatively, hexagonal grid spatial discretization has been proven to be superior to the square grid, attributed to its isotropic, consistent connectivity, uniform neighborhood. Taking these advantages into consideration, this paper explores the advantages of hexagonal grid discretization for isoline extraction in comparison with square grid. The comparisons show that a hexagonal grid performs better than a square grid, and it can extract finer isoline based on the same resolution. Result show that hexagonal grid can express the numerical differences between neighboring grid cells consistently and correctly, leading to improvements in isoline extraction. This paper demonstrates the significant impact of grid cell geometry on the quality of isoline obtained from grid-based geographical spatial data, providing new insights for spatial analysis of geographical data.