Con-Accessibility: Logit-based catchment area modeling for strategic airport system planning

National airport system plans serve as the primary programmatic documents employed by policy-makers to outline the roles of different airports and devise strategies for their coordinated and integrated development, encompassing economic, environmental, and social perspectives. This paper proposes a modeling framework to estimate the strength of each airport's influence and contribution to the surrounding territories, providing methodological foundation for assessing airport demand and delineating the scope of airport interactions. We propose a novel origin-based nested logit model of airport demand based on a comprehensive utility function-denoted as con-accessibility-integrating -integrating advanced metrics of ground accessibility and airport connectivity. To address the lack of extensive pairwise municipality-airport data, we cast the estimation problem as a nonlinear constrained least-squares optimization problem, solved via a differential evolution algorithm. The framework's applicability and insights are demonstrated in a real-world case study of the latest Italian national airport system plan. We highlight the model's capability in addressing three key policy questions: (i) characterizing airport catchments toward investigating the degree of overlap and airport interactions in serving contended areas; (ii) systematically quantifying the overall level of con-accessibility in any region to assess deficits or surpluses and pinpoint areas for strategic interventions; (iii) supporting the assessment and prioritization of various initiatives, including the upgrade of ground access networks, the expansion of airport supply, and the establishment of new airport facilities.