Abstract: An error model named the stochastic error process of curves is proposed to describe the errors of curves in GIS.In terms of the stochastic process,four characteristics concerning the local error of curves,namely,mean error function,standard error function,absolute mean error function and the correlation function of errors are put forward.The total error of a curve is expressed by a mean square integral of the stochastic error process.The probabilistic meanings and geometric meanings of the characteristics mentioned above are also discussed,and a scan digitizing test is designed.The result of the test shows that the system error in digitized map data is not negligible,and the errors of points on curves are chiefly dependent on the curvature and the concavity of the curves.