Contours may be directly collected from stereoscopic source by a compiler or may be generated from a lidar-derived TIN or DEM. The contours should be tested when specified as a deliverable whether they were directly compiled or derived from another data model, even if the source model meets required accuracies. This is because the accuracy of any derived product can be degraded by interpolation, generalization, or smoothing. Contour tests can be performed two ways. One method consists of plotting checkpoint locations in relationship with surrounding contours and mentally interpolating an elevation for that checkpoint from surrounding contours. Another method requires the contours to be converted to a TIN, from which elevations can be automatically interpreted with software. The TIN method is somewhat risky because TINing software cannot apply the rationale that may be required of the human during interpolation. Therefore, the TINing process may introduce additional error into the interpolated elevations. However, if the TIN test meets accuracy, one can be fairly confident that the contours meet accuracy. If the TIN accuracy fails, it may be necessary to perform the mental interpolation and retest.