The horizontal resolution is 90 meters (it varies with latitude) and based on this curve the rest was interpolated (It is assumed that in the United States it goes through 30 meters but it is useless to us). This functionality is visual in Google Maps, in Google Earth at the digital model level.
The source of this contour line that Google has integrated is the digital terrain model initially developed by NASA and continued by the USGS, which is known as SRTM-90m. This is activated in the left panel “Relief” and in the floating button you can activate or deactivate the view of curves. Google Maps added the highlight option to the map display, which includes contour lines from a certain zoom level.
