I'm trying to work with raster data from this source: http://www.soest.hawaii.edu/coasts/data/maui/index.html
I downloaded the DEMs from different islands and imported them into ArcGIS. But I can't seem to do anything with them. First, I tried to merge the different DEMs into one new raster. I also can't calculate a viewshed from a known point. I constantly get errors from the like of "dem not valid".
How do I convert them into formats I can actually work with?
I'm not too familiar with raster datasets.