| Abstract: | Previous evaluations of viewshed analyses have raised concerns about the accuracy and repeatability of the process. Digital elevation model (DEM) errors, the limited spatial resolution of DEMs, and differing algorithms employed by different GIS packages have all been suggested as possible sources for inaccuracy and non‐repeatability. This study compared a field surveyed viewshed to predicted viewsheds generated using a variety of software packages and DEM databases, some of which contained known amounts of error. We found that each of the factors suggested by previous authors contributes to errors in predicted viewsheds. DEM errors contribute most to the discrepancies between surveyed and predicted viewsheds, and the majority of their negative impact occurred at very low levels of DEM error. Differing algorithms used by different GIS packages also contribute significantly to surveyed/predicted viewshed discrepancies, but more importantly, result in predicted viewsheds that disagree with one other, thereby confounding comparisons of results generated with differing software systems. Finally, the spatial resolution of DEMs also has a significant effect on the degree of agreement between surveyed and predicted viewsheds, but the magnitude of this effect is not as great as are the effects produced by DEM errors. |
