Tile old adage that one picture Is worth a thousand words Is really a conservative estimate when applied to elevational data points. Digital elevation data presently being gathered or converted from previous mapping efforts afford valuable data for transportation planners, but these data are not readily usable. When these data are converted to an aerial photollke scene, they offer a valuable additional planning tool. Surrace simulation models based on US Geological Survey (USGS) digital elevation models were accomplished on a VAX 11/780 with a Vectrlx VX384 display. A Hermite curve technique was used to simulate tile surface configuration of the terrain. The terrain surface simulation was overlaid with USGS digital line graph data to show transpormtlon routes. In addition to vertical views, oblique views from any direction may be shown and the direction and vertical angle or the source or lighting may be chosen.

For some years, the US Geological Survey (USGS) has produced digital elevation model (DEM) and digital line graph (DLG) data for various parts of the United States. This ongoing program to make digital terrain data available for users recognizes the increasing importance of digital data for geographic data base systems. The DEM data together with a program such as Generalized Computer Aided Route Selection (GCARS) may be used to automatically locate alternate routes on the basis of terrain data (1). Other alternate routes based on such criteria as economic development or land cost may be developed and value weights may be applied to each data base to determine the best routes under various evaluation guidelines. Whether the route selection process is automated as outlined or is derived in some other maru, er, the various alternate routes together with existing transportation systems and other pertinent features are usually drawn on maps and possibly aerial photos for visual examination. Where topography contributes importantly to route location, topographical maps may be used to show the route's relationship to the terrain. Although such presentations are easily understood by engineers, the general public, other professionals and engineers alike, can more readily visualize topographic features when shown in three-dimensional form such as is possible with claylike models. However, the cost and time required to build such models