  Planning for the development of a 3rd generation global gravitational-wave
detector array is a multifaceted and complex effort that will necessarily need
a high level of community input. Interfacing to extant and new stakeholders in
the broader scientific constituencies is necessary to keep them aware of the
activities taking place in the ground-based gravitational-wave community and
receive input to inform and evolve the planning. In this report, we present the
approaches GWIC and gravitational-wave collaborations and projects should
consider taking to engage with broader community.
  This report is the fifth in a six part series of reports by the GWIC 3G
Subcommittee: i) Expanding the Reach of Gravitational Wave Observatories to the
Edge of the Universe, ii) The Next Generation Global Gravitational Wave
Observatory: The Science Book, iii) 3G R&D: R&D for the Next Generation of
Ground-based Gravitational Wave Detectors, iv) Gravitational Wave Data
Analysis: Computing Challenges in the 3G Era, v) Future Ground-based
Gravitational-wave Observatories: Synergies with Other Scientific Communities
(this report), and vi) An Exploration of Possible Governance Models for the
Future Global Gravitational-Wave Observatory Network.
