Question 1: Elevation, or
geometric height, is mainly used when referring to
points on the ________'s surface,
while altitude or geopotential height is
used for points above the surface, such as an aircraft in flight or a spacecraft in orbit.
Question 4: In a ________ (GIS), digital elevation models (DEM)
are commonly used to represent the surface (topography) of a place,
through a raster (grid) dataset of elevations.