  We determine the interstellar extinction in the selected high-latitude areas
of the sky based on Gaia EDR3 astrometry and photometry and spectroscopic data
from RAVE survey. We approximate the results with the cosecant law in each area
thus deriving the parameters of the barometric formula for different lines of
sight. The distribution of the parameters over the entire sky is described
using spherical harmonics. As a result, we get a mathematical description of
the interstellar visual extinction for different lines of sight and distances
from the Sun which can be used for estimating interstellar extinction.
