Rapid urbanization and intensive land-use transformation in Istanbul have generated increasing pressure on urban green infrastructure, resulting in pronounced spatial inequalities in access to public parks. As a rapidly expanding megacity with strong contrasts between compact urban cores and peripheral zones, Istanbul provides a representative case for examining the spatial effectiveness of urban parks within a complex metropolitan system. The study presents a systematic spatial assessment of urban parks as a key element of sustainable urban development across Istanbul’s 39 administrative districts. Applying a GIS-based analytical framework, the research integrates official green space inventories, administrative boundaries, and population data to evaluate both the quantitative availability of urban parks and their role in enhancing urban quality of life. A set of comparable spatial indicators is used, including the number and area of urban parks, their relative share of the district territory, their proportion within open and active green spaces, and park area per capita. The combined use of these indicators enables a multidimensional assessment that goes beyond simple measurements of green space quantity and captures functional and territorial differences between districts. The results demonstrate marked spatial imbalances in the distribution of urban parks. Higher levels of park provision are observed primarily in peripheral districts with lower building density, while central and densely urbanized districts show persistent deficits. Notably, eleven districts lack urban parks entirely; in these areas, green spaces are dominated by forested or non-urban green areas that do not provide equivalent recreational and social functions. These findings reveal a structural mismatch between the overall presence of green areas and the availability of accessible, functionally organized urban parks. The main contribution of this study is its integrative indicator-based approach, which distinguishes between different types of green spaces and explicitly identifies districts where the quantitative abundance of greenery does not translate into functional accessibility. By spatially highlighting zones of deficit and surplus, the research provides an empirical basis for more balanced and equity-oriented green infrastructure planning. The results support policy interventions focused on green regeneration of underutilized urban land, development of micro-parks in compact neighborhoods, and the strengthening of ecological connectivity as a pathway toward more resilient and socially inclusive urban environments.