The objective of this study was to describe data accuracy issues using digital elevation models (DEMs), which are increasingly used in GIS modeling. The issue of data accuracy brings a different perspective to the issue of GIS modeling and calls into question the usefulness of such data models as DEMs. Data accuracy was carried out by using the sensitivity of two types of DEMs on runoff volume. The two DEM formats used were 1:250,000-scale (1-degree) DEM data and 1:24,000-scale (7.5-minute) DEM data. A comparison of images of 7.5-minute and one-degree DEMs for the variable of elevation of the watershed was presented.