Regional Air Mobility (RAM) uses electric vertical take-off and landing (eVTOL) aircraft operating from vertiports. Whether a site is buildable and operationally useful depends on the intended aircraft and its environment through two channels: vehicle size scales the obstacle-protection geometry a site must clear, while for a fixed vehicle the local environment modulates the direction-dependent range over which the site can serve a network. Building on prior GIS-based suitability analysis for the Saxony case study, this paper assesses vertiport
location robustness along these two dimensions. Part I is a rule-based geometric screen that tests placement and Obstacle Free Volume (OFV) obstacle clearance across locations, design elevations, and headings, returning both buildability and a graded orientation robustness (the number of feasible headings), evaluated for two vehicle-size scenarios (Design D = 20 m and 12 m). Part II then characterises selected buildable sites:
a flight-performance model quantifies direction-dependent inbound and outbound range and derives graded coverage-robustness metrics capturing how terrain shrinks the robustly bidirectionally serviceable area. As range relevance is network-specific, Part II provides context-dependent decision support. The result is a reproducible framework that resolves vertiport location robustness into a vehicle-size-sensitive buildability dimension, verified down to orientation level against 3D obstacles, and an environment-sensitive coverage dimension, linking both for RAM vertiport planning.