The Data GM Portal Theme extension provides the official visual identity and user experience design for Greater Manchester’s Data GM open data portal, implementing regional branding, metropolitan styling, and Greater Manchester-specific functionality designed to serve the combined authority area covering ten metropolitan boroughs in North West England. This official regional theme incorporates Greater Manchester Combined Authority’s visual identity including official colors, logos, typography, and design patterns while maintaining compliance with UK government accessibility standards and regional digital service guidelines. The extension includes custom page layouts optimized for metropolitan regional data presentation, specialized templates for combined authority datasets, and integration with Greater Manchester’s digital infrastructure and UK government platforms. Advanced features include Greater Manchester localization with metropolitan regional considerations, specialized widgets for displaying combined authority data such as transport information, economic development statistics, regional planning data, and Greater Manchester-specific demographic and policy information reflecting the region’s devolved governance structure. The theme provides enhanced navigation structures tailored to Greater Manchester residents’ needs across all ten boroughs, quick access to frequently requested metropolitan regional data categories, and integration with Greater Manchester’s citizen engagement platforms and combined authority service systems. Customizations include specialized dataset categories for combined authority operations, enhanced search functionality with location-based filtering specific to Greater Manchester boroughs and districts, and mobile-optimized interfaces designed for citizen access to regional services and metropolitan information. Administrative features provide content management tools for Greater Manchester Combined Authority staff, workflow integration with regional governance systems, and analytics tracking for public data usage across the metropolitan region. Integration capabilities include connections to Greater Manchester’s regional databases, Transport for Greater Manchester systems, UK government services, and local community platforms for comprehensive regional civic engagement. Essential for Greater Manchester’s regional digital transformation initiatives, supporting combined authority transparency requirements, enhancing citizen access to regional government data, and promoting metropolitan community engagement through improved user experience that reflects Greater Manchester’s unique position as a pioneering devolved metropolitan region in the UK governance landscape.