Is 80 feet some sort of standard?
Based on USGS (Department of the Interior – United States Geological Survey) toopgraphic maps, where on a 7.5 min Quadrangle map, the contour interval is commonly 40 feet. Larger maps 15 min to 1'-2' maps the interval is commonly 80-100 feet.
All maps of the United States are commonly sourced from USGS based maps. I am certain Google or Google's map provider is using USGS base maps.