Let Δ mn be a grid partition of curves that divide a rectangular domain into a finite or countable number of cells inR 2, called type-1 triangulations. A kind of bivariate cubic splines is considered. A class of linear spline operators based on the bivariate cubic splines on the partition is given and shown to satisfy the identities about certain polynomials. In addition, these identities enable us to give error estimates for approximation from the entire space of the cubic spline function with the grid partition Δ mn .