Function sample_positions 

pub fn sample_positions(
    latitude: f64,
    longitude: f64,
    expansion_m: i64,
) -> Vec<(f64, f64)>

Every position to test against core geometry, the position itself first.

The position leads so a caller can stop on a core hit, and so the core-versus-expanded distinction falls out of the same loop: a hit at index zero is core, a hit anywhere later is expanded.