The presentation provides an overview of and key findings from the application of the SEI's architectural methods in the definition and assessment of an architecture for a Geographic Information System (GIS). This application resulted in the documentation of twenty-two quality attribute scenarios covering performance, availability, modifiability, security, testability and usability. Three design iterations were then performed, in accordance with the Attribute-Driven Design (ADD), producing an architecture, documented in two architectural views (Module and Component-and-Connector (C&C)). Thirty-eight distinct architectural design decisions were made; each contributed to the achievement of one or more quality attribute scenario. Finally, the GIS architecture was evaluated using the Architecture Trade-Off Analysis Method (ATAM), resulting in the identification of sixteen sensitivity points, ten tradeoff points, and thirteen risks, summarised in four risk themes. Lessons learnt from applying the SEI's architectural methods revealed that addressing GIS quality attributes systematically at the architectural stage facilitated an unambiguous record of the rationale, assumptions and dependencies of the critical technical decisions involved in achieving key quality drivers. This in turn improved the flexibility, adaptability and analysability of the architecture. Additionally, the GIS architectural process proved to be useful for teaching purposes. It is currently used as part of a postgraduate course in software architecture as an example of a systematically-defined architecture.