# emerge -pqv '=sci-geosciences/qgis-2.18.3-r1::gentoo'
[ebuild     U ] sci-geosciences/qgis-2.18.3-r1 [2.18.3] USE="georeferencer postgres python* -examples -grass -mapserver -oracle -webkit%" PYTHON_TARGETS="python2_7" 

!!! The following installed packages are masked:
- sys-kernel/gentoo-sources-4.9.2::gentoo (masked by: package.mask)
- www-client/chromium-57.0.2987.54::gentoo (masked by: package.mask)
For more information, see the MASKED PACKAGES section in the emerge
man page or refer to the Gentoo Handbook.