Who created the gtopo1km raster in the oregondata geodatabase? when was it created? in what units are the elevation values?

Water is a flat surface—For visualizations, all lakes and oceans should appear at their normal water levels. In some cases, the water bodies may be normalized to have an elevation value of zero. This is typically used for orthorectification.Water subsurface is valid—For hydrologic modeling, a civil engineer may want to know the topography of a river basin without any water present; therefore, the DEM includes bathymetric data.