Objective: This study aimed to quantify primary healthcare service deficits in Western Türkiye by comparing accessibility with capacity-adjusted coverage for Family Health Centers (FHCs), identify optimal, equity-focused locations for new FHCs using capacity-aware location-allocation modeling; and present a validated, reproducible Geographic Information Systems (GIS) based framework applicable to diverse national contexts.Method: Observational geographic analysis. GIS, location-allocation modeling, and joinpoint regression were applied across 11 Western Türkiye provinces. Accessibility, based on a 15-minute walking threshold was evaluated first. Coverage was then recalculated, incorporating FHC capacity, which is defined as a maximum of 2,500 people per Family Physician Unit. A scale-up analysis identified optimal locations to achieve 70% capacity-constrained coverage. Joinpoint regression assessed facility expansion efficiency.Results: While potential 15-minute walking accessibility appeared high in urban centers (e.g., Bursa 73.4%, İzmir 72.6%), enforcing capacity constraints drastically reduced effective coverage (e.g., Bursa 49.4%, İzmir 50.4%), revealing an average coverage gap exceeding 20 percentage points and exposing severe service pressure. Profound deficits were observed in rural districts (<20% coverage). Optimal locations for 1,074 new FHCs were identified. Gaps in absolute and percentage terms are summarized. Joinpoint analysis confirmed diminishing returns on expansion. Capacity gaps and geographic inequities remained robust in sensitivity analyses.Conclusion: Facility capacity, alongside proximity, determines effective PHC access in Western Türkiye, exacerbating urban-rural inequities. Planning based solely on distance is inadequate; incorporating capacity constraints is essential for assessment and equitable resource allocation. The demonstrated geospatial methodology provides a robust, adaptable normative tool for national PHC network planning.