Establishing a GIS toolbox to access urban verticality

• Developed a first step easy-to-use GIS toolbox for assessing legal vertical extension potential of existing buildings. • Integration of standardized geospatial data with parameters defined by the German building law context. • Enables city-wide pre-analysis and spatial mapping of vertical densification opportunities for sustainable land use. • Empowering local administrations in data-driven urban planning, land management, and housing strategies. • Demonstrated in Lüneburg, Germany, but transferable to cities balancing housing demand and land preservation. Cities today face the pressing challenge of meeting rising housing demand while preserving scarce land and environmental resources. Vertical extension presents a sustainable strategy to densify urban areas, minimizing outwards expansion and associated environmental impacts such as land take, habitat loss, and increased infrastructure demands. This study presents an innovative, user-friendly geospatial model designed to quantify the legal potential for vertical extension, demonstrated utilizing the city of Lüneburg, Lower Saxony, Germany as case study. Co-developed with local stakeholders and grounded in standardized data, the toolbox empowers planners and municipalities to independently explore, analyse, and visualize densification opportunities tailored to their specific context. By transforming complex spatial data into actionable insights, the approach offers a data-driven foundation to rethink urban planning and guide sustainable urban development.