One coverage standard is Multi-Order Coverage maps, described at http://www.ivoa.net/Documents/MOC/. MOC positions are always defined in ICRS equatorial coordinates.
MOC locations may be given as either the filename or the URL of
a MOC FITS file. Alternatively, they may be the identifier of a VizieR
table, for instance "V/139/sdss9
" (SDSS DR9).
A list of all the MOCs available from VizieR can
currently be found at
http://alasky.u-strasbg.fr/footprints/tables/vizier/.
You can search for VizieR table identifiers from the
VizieR web page
(http://vizier.u-strasbg.fr/);
note you must use
the table identifier (like "V/139/sdss9
")
and not the catalogue identifier (like "V/139
").