Layer identifier (for error messages)
Layer geometry type from config
Normalized flat style
OptionalfirstFeature: { properties?: Record<string, unknown> } | null
Optional first GeoJSON feature (for field heuristic)
OptionalsourceType: "geojson" | "vector"
"geojson" | "vector" (heuristic only runs on geojson)
Validates that required fill-extrusion style properties are present. Throws on missing required fields; logs warnings for suspicious config.