This article reports on the initial development of a generic framework for integrating Geographic Information Systems (GIS) with Massive Multi-player Online Gaming (MMOG) technology to support the integrated modeling of human-environment resource management and decision-making. We review Web 2.0 concepts, online maps, and games as key technologies to realize a participatory construction of spatial simulation and decision making practices. Through a design-based research approach we develop a prototype framework, "GeoGame", that allows users to play board-game-style simulations on top of an online map. Through several iterations we demonstrate the implementation of a range of design artifacts including: realtime, multi-user editing of online maps, web services, game lobby, user-modifiable rules and scenarios building, chat, discussion, and market transactions. Based on observational, analytical, experimental and functional evaluations of design artifacts as well as a literature review, we argue that a MMO GeoGame-framework offers a viable approach to address the complex dynamics of human-environmental systems that require a simultaneous reconciliation of both top-down and bottom-up decision making where stakeholders are an integral part of a modeling environment. Further