Technical interoperability has provided geographic information communities with substantial improvements for constructing GIS capable of very low friction and dynamic data exchanges. These technical advances stand to provide substantial advantages for sharing geographic information, however reaping these advantages in highly heterogeneous operational and organizational environments requires the understanding and resolution of semantic differences. While the OpenGIS consortium has made important progress on technical interoperability, semantic interoperability still remains an unpassed hurdle for efforts to share geographic information across organizational and institutional boundaries at the local, regional, and other levels. Identifying and resolving semantic interoperability issues is especially pertinent for data sharing and considering future developments of standards. This paper presents an overview of semantic interoperability and through case studies shows the breadth and depth of issues and approaches in different countries and at different levels of organizations. These cases illustrate the importance of developing flexible approaches to practical data sharing problems that merge semantical with technical considerations. Based on our examinations of semantic issues and approaches in ongoing research projects, we propose cognitive, computer science, and socio-technical frameworks for examining semantic interoperability.