RTree-based spatial map. Use whenever you have some spatial data you'd like assign some values to, then lookup those values later.
use geo::polygon;
let polygons = vec![polygon![
(x: 0f32, y: 0f32),
(x: 5f32, y: 5f32),
(x: 5f32, y: 0f32),
]];
let defs = vec![(polygons, 1)];
let db = GeoIndex::new(defs, 0);
assert_eq!(db.lookup_coords(Some(&Point::new(2f32, 1f32))), &1);