There are (at least) three formal ways in which ISSS members can formally interact with other like-mind systems thinkers in the ISSS community.
SIGs -- which mean Special Integration Groups, not Special Interest Groups -- come together to share knowledge in common pursuits. The discussions are meant to be expansive, not reductive. SIGs bring together a large part of the content at the annual meetings.
Regional Chapters take advantage of close geographic proximity to have face-to-face events close to home. Since the annual meetings change venue from one location to another, every year, Chapters sometimes host local satellite conferences to share their ideas in a smaller group.
Since many of us are members and/or volunteers in multiple professional organizations, formal Liaisons can help members create bridges to external communities. Other organizations may share mutual interests, and/or exchanges of knowledge.
By the ISSS Bylaws, the chairs of active units have a voice in the ISSS Council. They represent the interests and opinions of their constituents in the larger organizational context of ISSS decision-making.