  The observation of gravitational wave signals from binary black hole mergers
has established the field of gravitational wave astronomy. It is expected that
future networks of gravitational wave detectors will possess great potential in
probing various aspects of astronomy. An important consideration for successive
improvement of current detectors or establishment on new sites is knowledge of
the minimum number of detectors required to perform precision astronomy. We
attempt to answer this question by assessing ability of future detector
networks in detecting and localizing binary neutron stars mergers in the sky.
This is an important aspect as a good localization ability is crucial for many
of the scientific goals of gravitational wave astronomy, such as
electromagnetic follow-up, measuring the properties of compact binaries
throughout cosmic history, and cosmology. We find that although two detectors
at improved sensitivity are sufficient to get a substantial increase in the
number of observed signals, at least three detectors of comparable sensitivity
are required to localize majority of the signals, typically to within around 10
deg$^{2}$ --- adequate for follow-up with most wide field of view optical
telescopes.
