diff --git a/demo/src/lib.rs b/demo/src/lib.rs
index ab93937..c8e105e 100644
--- a/demo/src/lib.rs
+++ b/demo/src/lib.rs
@@ -1,7 +1,7 @@
 use wasm_bindgen::prelude::*;
 use web_sys;
 use rand::prelude::*;
-use mapgen::{Map, MapBuilder, geometry::Point};
+use mapgen::{Map, MapBuilder, NoData, geometry::Point};
 use mapgen::filter::*;
 use mapgen::metric;
 
@@ -19,7 +19,7 @@ pub struct World {
     width: u32,
     height: u32,
     tiles: Vec<Cell>,
-    map: Map,
+    map: Map<NoData>,
 }
 
 #[wasm_bindgen]
@@ -32,7 +32,7 @@ pub struct Position {
 #[wasm_bindgen]
 impl World {
     
-    fn new(width: u32, height: u32, map: Map) -> World {
+    fn new(width: u32, height: u32, map: Map<NoData>) -> World {
         let tiles = (0..map.tiles.len())
             .map(|i| if map.tiles[i].is_walkable() {Cell::Floor} else {Cell::Wall})
             .collect();
@@ -176,7 +176,7 @@ impl World {
         div.set_inner_html(&info);
     }
     
-    fn print_map_metrics(map: &Map) {
+    fn print_map_metrics(map: &Map<NoData>) {
         let window = web_sys::window().expect("no global `window` exists");
         let document = window.document().expect("should have a document on window");
         let div = document.get_element_by_id("map-metrics").expect("Need div with id: map-metrics");
diff --git a/examples/bsp_interior.rs b/examples/bsp_interior.rs
index 2b87425..185b172 100644
--- a/examples/bsp_interior.rs
+++ b/examples/bsp_interior.rs
@@ -4,7 +4,7 @@ use mapgen::*;
 
 fn main() {
     let mut rng = StdRng::seed_from_u64(907647352);
-    let gen = BspInterior::new();
+    let gen = BspInterior::<NoData>::new();
     let map = gen.modify_map(&mut rng, &Map::new(20, 10));
     println!("{:}", &map);
 }
\ No newline at end of file
diff --git a/examples/bsp_rooms.rs b/examples/bsp_rooms.rs
index cf3ca9b..f960b67 100644
--- a/examples/bsp_rooms.rs
+++ b/examples/bsp_rooms.rs
@@ -6,7 +6,7 @@ use mapgen::*;
 fn main() {
     let system_time = SystemTime::now().duration_since(UNIX_EPOCH).expect("Can't access system time");
     let mut rng = StdRng::seed_from_u64(system_time.as_millis() as u64);
-    let gen = BspRooms::new();
+    let gen = BspRooms::<NoData>::new();
     let map = gen.modify_map(&mut rng, &Map::new(80, 50));
     println!("{:}", &map);
 }
\ No newline at end of file
diff --git a/examples/example1.rs b/examples/example1.rs
index 32efff9..fcaa7a3 100644
--- a/examples/example1.rs
+++ b/examples/example1.rs
@@ -1,5 +1,6 @@
 use mapgen::{
     MapBuilder,
+    NoData,
     filter::{
         NoiseGenerator, 
         CellularAutomata,
@@ -12,7 +13,7 @@ use mapgen::{
 
 
 fn main() {
-    let map = MapBuilder::new(20, 20)
+    let map = MapBuilder::<NoData>::new(20, 20)
         .with(NoiseGenerator::uniform())
         .with(CellularAutomata::new())
         .with(AreaStartingPosition::new(XStart::CENTER, YStart::CENTER))
diff --git a/src/dijkstra.rs b/src/dijkstra.rs
index a0e4cb0..3ee1d6d 100644
--- a/src/dijkstra.rs
+++ b/src/dijkstra.rs
@@ -25,25 +25,26 @@
 //! ---
 //! 
 
-use std::collections::VecDeque;
+use std::{collections::VecDeque, marker::PhantomData};
 use std::f32::MAX;
-use super::map::Map;
+use super::map::{BuilderData, Map};
 
 
 /// Representation of a Dijkstra flow map.
 /// map is a vector of floats, having a size equal to size_x * size_y (one per tile).
 /// size_x and size_y are stored for overflow avoidance.
 /// max_depth is the maximum number of iterations this search shall support.
-pub struct DijkstraMap {
+pub struct DijkstraMap<D> {
     pub tiles: Vec<f32>,
     size_x: usize,
     size_y: usize,
     max_depth: f32,
+    phantom: PhantomData<D>,
 }
 
-impl DijkstraMap {
+impl<D: BuilderData> DijkstraMap<D> {
     //! Construct a new Dijkstra map, ready to run. 
-    pub fn new(map: &Map) -> DijkstraMap {
+    pub fn new(map: &Map<D>) -> DijkstraMap<D> {
         let len =  map.width * map.height;
         let tiles = vec![MAX; len];
         let mut d = DijkstraMap {
@@ -51,6 +52,7 @@ impl DijkstraMap {
             size_x: map.width,
             size_y: map.height,
             max_depth: len as f32,
+            phantom: PhantomData,
         };
         d.build(map);
         d
@@ -61,7 +63,7 @@ impl DijkstraMap {
     /// depth is further than the current depth.
     /// WARNING: Will give incorrect results when used with non-uniform exit costs. Much slower
     /// algorithm required to support that.
-    fn build(&mut self, map: &Map) {
+    fn build(&mut self, map: &Map<D>) {
         let mapsize: usize = (self.size_x * self.size_y) as usize;
         let mut open_list: VecDeque<((usize, usize), f32)> = VecDeque::with_capacity(mapsize);
 
@@ -97,7 +99,7 @@ impl DijkstraMap {
 mod tests {
     use super::*;
     use crate::geometry::Point;
-    use crate::map::Map;
+    use crate::map::{Map, NoData};
 
     #[test]
     fn test_culling() {
@@ -106,7 +108,7 @@ mod tests {
         # #      #
         ##########
         ";
-        let mut map = Map::from_string(map_str);
+        let mut map = Map::<NoData>::from_string(map_str);
         map.starting_point = Some(Point::new(8, 1));
         let dm = DijkstraMap::new(&map);
 
@@ -134,7 +136,7 @@ mod tests {
         #  #
         ####
         ";
-        let mut map = Map::from_string(map_str);
+        let mut map = Map::<NoData>::from_string(map_str);
         map.starting_point = Some(Point::new(2, 2));
         let dm = DijkstraMap::new(&map);
         let expected = [MAX, MAX, MAX, MAX,
@@ -153,7 +155,7 @@ mod tests {
         #  #     #
         ##########
         ";
-        let mut map = Map::from_string(map_str);
+        let mut map = Map::<NoData>::from_string(map_str);
         map.starting_point = Some(Point::new(8, 2));
         let dm = DijkstraMap::new(&map);
         let expected = [MAX, MAX, MAX, MAX, MAX, MAX, MAX, MAX, MAX, MAX, 
diff --git a/src/filter/bsp_interior.rs b/src/filter/bsp_interior.rs
index 996f01f..6db69e7 100644
--- a/src/filter/bsp_interior.rs
+++ b/src/filter/bsp_interior.rs
@@ -6,13 +6,13 @@
 //! Example generator usage:
 //! ```
 //! use rand::prelude::*;
-//! use mapgen::{Map, MapFilter};
+//! use mapgen::{Map, MapFilter, NoData};
 //! use mapgen::filter::{
 //!     BspInterior
 //! };
 //! 
 //! let mut rng = StdRng::seed_from_u64(100);
-//! let gen = BspInterior::new();
+//! let gen = BspInterior::<NoData>::new();
 //! let map = gen.modify_map(&mut rng, &Map::new(80, 50));
 //! 
 //! assert_eq!(map.width, 80);
@@ -20,32 +20,36 @@
 //! ```
 //! 
 
+use std::marker::PhantomData;
+
 use rand::prelude::*;
-use crate::MapFilter;
+use crate::{BuilderData, MapFilter};
 use crate::geometry::{Point, Rect};
 use crate::random::Rng;
 use crate::Map;
 
 
-pub struct BspInterior {
+pub struct BspInterior<D: BuilderData> {
     min_room_size: usize,
+    phantom: PhantomData<D>,
 }
 
-impl MapFilter for BspInterior {
-    fn modify_map(&self, rng: &mut StdRng, map: &Map) -> Map {
+impl<D: BuilderData> MapFilter<D> for BspInterior<D> {
+    fn modify_map(&self, rng: &mut StdRng, map: &Map<D>) -> Map<D> {
         self.build(rng, map)
     }
 }
 
-impl BspInterior {
+impl<D: BuilderData> BspInterior<D> {
 
-    pub fn new() -> Box<BspInterior> {
+    pub fn new() -> Box<BspInterior<D>> {
         Box::new(BspInterior{
             min_room_size: 8,
+            phantom: PhantomData,
         })
     }
 
-    fn build(&self, rng: &mut StdRng, map: &Map) -> Map {
+    fn build(&self, rng: &mut StdRng, map: &Map<D>) -> Map<D> {
         let mut new_map = map.clone();
         let mut rects: Vec<Rect> = Vec::new();
         rects.push( Rect::new(1, 1, new_map.width-2, new_map.height-2) ); 
@@ -114,12 +118,12 @@ impl BspInterior {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::{Map};
+    use crate::{Map, map::NoData};
 
     #[test]
     fn no_corridors_on_borders() {
          let mut rng = StdRng::seed_from_u64(907647352);
-        let gen = BspInterior::new();
+        let gen = BspInterior::<NoData>::new();
         let map = gen.modify_map(&mut rng, &Map::new(80, 50));
         for i in 0..80 {
             assert!(map.at(i, 0).is_blocked());
diff --git a/src/filter/bsp_rooms.rs b/src/filter/bsp_rooms.rs
index 8028eda..8639408 100644
--- a/src/filter/bsp_rooms.rs
+++ b/src/filter/bsp_rooms.rs
@@ -6,11 +6,11 @@
 //! Example generator usage:
 //! ```
 //! use rand::prelude::*;
-//! use mapgen::{Map, MapFilter};
+//! use mapgen::{Map, MapFilter, NoData};
 //! use mapgen::filter::BspRooms;
 //! 
 //! let mut rng = StdRng::seed_from_u64(100);
-//! let gen = BspRooms::new();
+//! let gen = BspRooms::<NoData>::new();
 //! let map = gen.modify_map(&mut rng, &Map::new(80, 50));
 //! 
 //! assert_eq!(map.width, 80);
@@ -18,31 +18,36 @@
 //! ```
 //! 
 
+use std::marker::PhantomData;
+
 use rand::prelude::*;
+use crate::BuilderData;
 use crate::MapFilter;
 use crate::geometry::Rect;
 use crate::random::Rng;
 use crate::Map;
 
 
-pub struct BspRooms {
+pub struct BspRooms<D: BuilderData> {
     max_split: usize,
+    phantom: PhantomData<D>,
 }
 
-impl MapFilter for BspRooms {
-    fn modify_map(&self, rng: &mut StdRng, map: &Map)  -> Map {
+impl<D: BuilderData> MapFilter<D> for BspRooms<D> {
+    fn modify_map(&self, rng: &mut StdRng, map: &Map<D>)  -> Map<D> {
         self.build_rooms(map, rng)
     }
 }
 
-impl BspRooms {
-    pub fn new() -> Box<BspRooms> {
+impl<D: BuilderData> BspRooms<D> {
+    pub fn new() -> Box<BspRooms<D>> {
         Box::new(BspRooms {
             max_split: 240,
+            phantom: PhantomData,
         })
     }
 
-    fn build_rooms(&self, map: &Map, rng : &mut StdRng) -> Map {
+    fn build_rooms(&self, map: &Map<D>, rng : &mut StdRng) -> Map<D> {
         let mut new_map = map.clone();
         let mut rects: Vec<Rect> = Vec::new();
         // Start with a single map-sized rectangle
@@ -102,7 +107,7 @@ impl BspRooms {
         result
     }
 
-    fn is_possible(&self, rect: Rect, map: &Map) -> bool {
+    fn is_possible(&self, rect: Rect, map: &Map<D>) -> bool {
         let mut expanded = rect;
         expanded.x1 -= 2;
         expanded.x2 += 2;
@@ -139,12 +144,12 @@ impl BspRooms {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::map::Map;
+    use crate::map::{Map, NoData};
 
     #[test]
     fn no_corridors_on_borders() {
          let mut rng = StdRng::seed_from_u64(907647352);
-        let gen = BspRooms::new();
+        let gen = BspRooms::<NoData>::new();
         let map = gen.modify_map(&mut rng, &Map::new(80, 50));
         for i in 0..80 {
             assert!(map.at(i, 0).is_blocked());
diff --git a/src/filter/cellular_automata.rs b/src/filter/cellular_automata.rs
index 365ab61..d35eff3 100644
--- a/src/filter/cellular_automata.rs
+++ b/src/filter/cellular_automata.rs
@@ -9,11 +9,11 @@
 //! Example usage:
 //! ```
 //! use rand::prelude::*;
-//! use mapgen::{Map, MapFilter};
+//! use mapgen::{Map, MapFilter, NoData};
 //! use mapgen::filter::CellularAutomata;
 //! 
 //! let mut rng = StdRng::seed_from_u64(100);
-//! let gen = CellularAutomata::new();
+//! let gen = CellularAutomata::<NoData>::new();
 //! let map = gen.modify_map(&mut rng, &Map::new(80, 50));
 //! 
 //! assert_eq!(map.width, 80);
@@ -21,30 +21,37 @@
 //! ```
 //! 
 
+use std::marker::PhantomData;
+
 use rand::prelude::*;
+use crate::BuilderData;
 use crate::MapFilter;
 use crate::{Map, Tile};
 
 
 /// Map filter
-pub struct CellularAutomata {
+pub struct CellularAutomata<D: BuilderData> {
     num_iteraction: u32,
+    phantom: PhantomData<D>,
 }
 
-impl MapFilter for CellularAutomata {
-    fn modify_map(&self, _rng: &mut StdRng, map: &Map)  -> Map {
+impl<D: BuilderData> MapFilter<D> for CellularAutomata<D> {
+    fn modify_map(&self, _rng: &mut StdRng, map: &Map<D>)  -> Map<D> {
         self.build(map)
     }
 }
 
-impl CellularAutomata {
+impl<D: BuilderData> CellularAutomata<D> {
     /// Create generator which will create map with the given dimension.
-    pub fn new() -> Box<CellularAutomata> {
-        Box::new(CellularAutomata { num_iteraction: 15})
+    pub fn new() -> Box<CellularAutomata<D>> {
+        Box::new(CellularAutomata {
+            num_iteraction: 15,
+            phantom: PhantomData,
+        })
     }
 
     /// Generate map
-    fn build(&self, map: &Map) -> Map {
+    fn build(&self, map: &Map<D>) -> Map<D> {
         let mut new_map = map.clone();
         for _ in 0..self.num_iteraction {
             new_map = apply_iteration(&new_map);
@@ -55,7 +62,7 @@ impl CellularAutomata {
 
 }
 
-fn apply_iteration(map: &Map) -> Map {
+fn apply_iteration<D: BuilderData>(map: &Map<D>) -> Map<D> {
     let mut new_map = map.clone();
 
     for y in 1..map.height-1 {
@@ -85,11 +92,13 @@ fn apply_iteration(map: &Map) -> Map {
 /// ------------------------------------------------------------------------------------------------
 #[cfg(test)]
 mod tests {
+    use crate::map::NoData;
+
     use super::*;
 
     #[test]
     fn test_iteration_wal() {
-        let map = Map::new(3, 3);
+        let map = Map::<NoData>::new(3, 3);
         let new_map = apply_iteration(&map);
         assert!(new_map.at(1, 1).is_blocked());
     }
@@ -97,7 +106,7 @@ mod tests {
 
     #[test]
     fn test_iteration_floor() {
-        let mut map = Map::new(3, 3);
+        let mut map = Map::<NoData>::new(3, 3);
         for i in 0..3 {
             for j in 0..2 {
                 map.set_tile(i, j, Tile::floor());
diff --git a/src/filter/cull_unreachable.rs b/src/filter/cull_unreachable.rs
index 6f8c6e8..c180341 100644
--- a/src/filter/cull_unreachable.rs
+++ b/src/filter/cull_unreachable.rs
@@ -4,28 +4,34 @@
 //! It will add wall on every tile which is not accessible from the starting point.
 //! 
 
+use std::marker::PhantomData;
+
 use rand::prelude::StdRng;
 use crate::MapFilter;
-use crate::{Map, Tile};
+use crate::{BuilderData, Map, Tile};
 use crate::dijkstra::DijkstraMap;
 
 
 /// Remove unreachable areas from the map.
-pub struct CullUnreachable {}
+pub struct CullUnreachable<D: BuilderData> {
+    phantom: PhantomData<D>,
+}
 
-impl MapFilter for CullUnreachable {
-    fn modify_map(&self, _: &mut StdRng, map: &Map)  -> Map {
+impl<D: BuilderData> MapFilter<D> for CullUnreachable<D> {
+    fn modify_map(&self, _: &mut StdRng, map: &Map<D>)  -> Map<D> {
         self.build(map)
     }
 }
 
-impl CullUnreachable {
+impl<D: BuilderData> CullUnreachable<D> {
     #[allow(dead_code)]
-    pub fn new() -> Box<CullUnreachable> {
-        Box::new(CullUnreachable{})
+    pub fn new() -> Box<CullUnreachable<D>> {
+        Box::new(CullUnreachable {
+            phantom: PhantomData,
+        })
     }
 
-    fn build(&self, map: &Map) -> Map {
+    fn build(&self, map: &Map<D>) -> Map<D> {
         let mut new_map = map.clone();
 
         let dijkstra_map = DijkstraMap::new(map);
@@ -51,7 +57,7 @@ mod tests {
     use super::*;
     use super::MapFilter;
     use crate::geometry::Point;
-    use crate::map::Map;
+    use crate::map::{Map, NoData};
 
     #[test]
     fn test_culling() {
@@ -60,14 +66,14 @@ mod tests {
         #  #     #
         ##########
         ";
-        let mut map = Map::from_string(map_str);
+        let mut map = Map::<NoData>::from_string(map_str);
         map.starting_point = Some(Point::new(9, 1));
         let expected_map_str = "
         ##########
         ####     #
         ##########
         ";
-        let expected_map = Map::from_string(expected_map_str);
+        let expected_map = Map::<NoData>::from_string(expected_map_str);
 
 
         let modifier = CullUnreachable::new();
diff --git a/src/filter/distant_exit.rs b/src/filter/distant_exit.rs
index 498d577..9d622d3 100644
--- a/src/filter/distant_exit.rs
+++ b/src/filter/distant_exit.rs
@@ -5,7 +5,9 @@
 //! 
 
 use std::f32;
+use std::marker::PhantomData;
 use rand::prelude::StdRng;
+use crate::BuilderData;
 use crate::geometry::Point;
 use crate::MapFilter;
 use crate::Map;
@@ -13,21 +15,25 @@ use crate::dijkstra::DijkstraMap;
 
 
 /// Add exist position to the map based on the distance from the start point.
-pub struct DistantExit {} 
+pub struct DistantExit<D: BuilderData> {
+    phantom: PhantomData<D>,
+}
 
-impl MapFilter for DistantExit {
-    fn modify_map(&self, _: &mut StdRng, map: &Map)  -> Map {
+impl<D: BuilderData> MapFilter<D> for DistantExit<D> {
+    fn modify_map(&self, _: &mut StdRng, map: &Map<D>)  -> Map<D> {
         self.build(map)
     }
 }
 
-impl DistantExit {
+impl<D: BuilderData> DistantExit<D> {
     #[allow(dead_code)]
-    pub fn new() -> Box<DistantExit> {
-        Box::new(DistantExit{})
+    pub fn new() -> Box<DistantExit<D>> {
+        Box::new(DistantExit {
+            phantom: PhantomData,
+        })
     }
 
-    fn build(&self, map: &Map) -> Map {
+    fn build(&self, map: &Map<D>) -> Map<D> {
         let mut new_map = map.clone();
 
         let mut best_idx = 0;
@@ -55,7 +61,7 @@ mod tests {
     use super::*;
     use super::MapFilter;
     use crate::geometry::Point;
-    use crate::map::Map;
+    use crate::map::{Map, NoData};
 
     #[test]
     fn test_exit() {
@@ -65,7 +71,7 @@ mod tests {
         #  #     #
         ##########
         ";
-        let mut map = Map::from_string(map_str);
+        let mut map = Map::<NoData>::from_string(map_str);
         map.starting_point = Some(Point::new(9, 2));
 
         let modifier = DistantExit::new();
diff --git a/src/filter/drunkard.rs b/src/filter/drunkard.rs
index 9c8b341..17b4661 100644
--- a/src/filter/drunkard.rs
+++ b/src/filter/drunkard.rs
@@ -1,11 +1,11 @@
 //! Example generator usage:
 //! ```
 //! use rand::prelude::*;
-//! use mapgen::{Map, MapFilter};
+//! use mapgen::{Map, MapFilter, NoData};
 //! use mapgen::filter::DrunkardsWalk;
 //! 
 //! let mut rng = StdRng::seed_from_u64(100);
-//! let gen = DrunkardsWalk::open_area();
+//! let gen = DrunkardsWalk::<NoData>::open_area();
 //! let map = gen.modify_map(&mut rng, &Map::new(80, 50));
 //! 
 //! assert_eq!(map.width, 80);
@@ -13,9 +13,12 @@
 //! ```
 //! 
 
+use std::marker::PhantomData;
+
 use rand::prelude::*;
 use crate::MapFilter;
 use crate::{
+    BuilderData,
     map::{Map, Symmetry, Tile},
     geometry::Point,
     random::Rng
@@ -25,57 +28,59 @@ use crate::{
 #[derive(PartialEq, Copy, Clone)]
 pub enum DrunkSpawnMode { StartingPoint, Random }
 
-pub struct DrunkardsWalk {
+pub struct DrunkardsWalk<D: BuilderData> {
     spawn_mode : DrunkSpawnMode,
     drunken_lifetime : i32,
     floor_percent: f32,
     brush_size: usize,
-    symmetry: Symmetry
+    symmetry: Symmetry,
+    phantom: PhantomData<D>,
 }
 
-impl MapFilter for DrunkardsWalk {
-    fn modify_map(&self, rng: &mut StdRng, map: &Map)  -> Map {
+impl<D: BuilderData> MapFilter<D> for DrunkardsWalk<D> {
+    fn modify_map(&self, rng: &mut StdRng, map: &Map<D>)  -> Map<D> {
         self.build(rng, map)
     }
 }
 
-impl DrunkardsWalk {
+impl<D: BuilderData> DrunkardsWalk<D> {
     pub fn new( spawn_mode: DrunkSpawnMode, 
                 drunken_lifetime: i32, 
                 floor_percent: f32,
                 brush_size: usize, 
-                symmetry: Symmetry) -> Box<DrunkardsWalk>
+                symmetry: Symmetry) -> Box<DrunkardsWalk<D>>
     {
         Box::new(DrunkardsWalk{
             spawn_mode,
             drunken_lifetime,
             floor_percent,
             brush_size,
-            symmetry
+            symmetry,
+            phantom: PhantomData,
         })
     }
 
-    pub fn open_area() -> Box<DrunkardsWalk> {
+    pub fn open_area() -> Box<DrunkardsWalk<D>> {
         Self::new(DrunkSpawnMode::StartingPoint, 400, 0.5, 1, Symmetry::None)
     }
 
-    pub fn open_halls() -> Box<DrunkardsWalk> {
+    pub fn open_halls() -> Box<DrunkardsWalk<D>> {
         Self::new(DrunkSpawnMode::Random, 400, 0.5, 1, Symmetry::None)
     }
 
-    pub fn winding_passages() -> Box<DrunkardsWalk> {
+    pub fn winding_passages() -> Box<DrunkardsWalk<D>> {
         Self::new(DrunkSpawnMode::Random, 400, 0.4, 1, Symmetry::None)
     }
 
-    pub fn fat_passages() -> Box<DrunkardsWalk> {
+    pub fn fat_passages() -> Box<DrunkardsWalk<D>> {
         Self::new(DrunkSpawnMode::Random, 400, 0.4, 2, Symmetry::None)
     }
 
-    pub fn fearful_symmetry() -> Box<DrunkardsWalk> {
+    pub fn fearful_symmetry() -> Box<DrunkardsWalk<D>> {
         Self::new(DrunkSpawnMode::Random, 400, 0.4, 1, Symmetry::Both)
     }
     
-    fn build(&self, rng: &mut StdRng, map: &Map) -> Map {
+    fn build(&self, rng: &mut StdRng, map: &Map<D>) -> Map<D> {
         let mut new_map = map.clone();
         // Set a central starting point
         let starting_position = Point::new( new_map.width / 2, new_map.height / 2 );
diff --git a/src/filter/maze.rs b/src/filter/maze.rs
index eab7d9f..b915fce 100644
--- a/src/filter/maze.rs
+++ b/src/filter/maze.rs
@@ -1,11 +1,11 @@
 //! Example generator usage:
 //! ```
 //! use rand::prelude::*;
-//! use mapgen::{Map, MapFilter};
+//! use mapgen::{Map, MapFilter, NoData};
 //! use mapgen::filter::MazeBuilder;
 //! 
 //! let mut rng = StdRng::seed_from_u64(100);
-//! let gen = MazeBuilder::new();
+//! let gen = MazeBuilder::<NoData>::new();
 //! let map = gen.modify_map(&mut rng, &Map::new(80, 50));
 //! 
 //! assert_eq!(map.width, 80);
@@ -13,29 +13,35 @@
 //! ```
 //! 
 
+use std::marker::PhantomData;
+
 use rand::prelude::*;
 use crate::MapFilter;
 use crate::{
-    map::{Map, Tile},
+    map::{BuilderData, Map, Tile},
     random::Rng
 };
 
 
-pub struct MazeBuilder {}
+pub struct MazeBuilder<D: BuilderData> {
+    phantom: PhantomData<D>,
+}
 
-impl MapFilter for MazeBuilder {
-    fn modify_map(&self, rng: &mut StdRng, map: &Map)  -> Map {
+impl<D: BuilderData> MapFilter<D> for MazeBuilder<D> {
+    fn modify_map(&self, rng: &mut StdRng, map: &Map<D>)  -> Map<D> {
         self.build(rng, map)
     }
 }
 
-impl MazeBuilder {
-    pub fn new() -> Box<MazeBuilder> {
-        Box::new(MazeBuilder{})
+impl<D: BuilderData> MazeBuilder<D> {
+    pub fn new() -> Box<MazeBuilder<D>> {
+        Box::new(MazeBuilder {
+            phantom: PhantomData,
+        })
     }
 
     #[allow(clippy::map_entry)]
-    fn build(&self, rng: &mut StdRng, map: &Map) -> Map {
+    fn build(&self, rng: &mut StdRng, map: &Map<D>) -> Map<D> {
         let mut new_map = map.clone();
         let mut maze = Grid::new((map.width as i32/ 2)-2, (map.height as i32/ 2)-2, rng);
         maze.generate_maze(&mut new_map);
@@ -91,24 +97,26 @@ impl Cell {
     }
 }
 
-struct Grid<'a> {
+struct Grid<'a, D: BuilderData> {
     width: i32,
     height: i32,
     cells: Vec<Cell>,
     backtrace: Vec<usize>,
     current: usize,
-    rng : &'a mut StdRng
+    rng : &'a mut StdRng,
+    phantom: PhantomData<D>,
 }
 
-impl<'a> Grid<'a> {
-    fn new(width: i32, height:i32, rng: &mut StdRng) -> Grid {
+impl<'a, D: BuilderData> Grid<'a, D> {
+    fn new(width: i32, height:i32, rng: &mut StdRng) -> Grid<D> {
         let mut grid = Grid{
             width,
             height,
             cells: Vec::new(),
             backtrace: Vec::new(),
             current: 0,
-            rng
+            rng,
+            phantom: PhantomData,
         };
 
         for row in 0..height {
@@ -162,7 +170,7 @@ impl<'a> Grid<'a> {
         None
     }
 
-    fn generate_maze(&mut self, map: &mut Map) {
+    fn generate_maze(&mut self, map: &mut Map<D>) {
         let mut i = 0;
         loop {
             self.cells[self.current].visited = true;
@@ -199,7 +207,7 @@ impl<'a> Grid<'a> {
         }
     }
 
-    fn copy_to_map(&self, map: &mut Map) {
+    fn copy_to_map(&self, map: &mut Map<D>) {
         // Clear the map
         for i in map.tiles.iter_mut() { *i = Tile::wall(); }
 
diff --git a/src/filter/noise_generator.rs b/src/filter/noise_generator.rs
index d7d6a7c..ec8a24a 100644
--- a/src/filter/noise_generator.rs
+++ b/src/filter/noise_generator.rs
@@ -4,11 +4,11 @@
 //! Example usage:
 //! ```
 //! use rand::prelude::*;
-//! use mapgen::{Map, MapFilter};
+//! use mapgen::{Map, MapFilter, NoData};
 //! use mapgen::filter::NoiseGenerator;
 //! 
 //! let mut rng = StdRng::seed_from_u64(100);
-//! let gen = NoiseGenerator::uniform();
+//! let gen = NoiseGenerator::<NoData>::uniform();
 //! let map = gen.modify_map(&mut rng, &Map::new(80, 50));
 //! 
 //! assert_eq!(map.width, 80);
@@ -16,39 +16,44 @@
 //! ```
 //! 
 
+use std::marker::PhantomData;
+
 use rand::prelude::*;
 use crate::MapFilter;
-use crate::{Map, Tile};
+use crate::{BuilderData, Map, Tile};
 
 
 /// Map noise generator
-pub struct NoiseGenerator {
+pub struct NoiseGenerator<D: BuilderData> {
     prob: f32,
+    phantom: PhantomData<D>,
 }
 
-impl MapFilter for NoiseGenerator {
-    fn modify_map(&self, rng: &mut StdRng, map: &Map)  -> Map {
+impl<D: BuilderData> MapFilter<D> for NoiseGenerator<D> {
+    fn modify_map(&self, rng: &mut StdRng, map: &Map<D>)  -> Map<D> {
         self.build(map, rng)
     }
 }
 
-impl NoiseGenerator {
+impl<D: BuilderData> NoiseGenerator<D> {
     /// Create noise with custom probability
-    pub fn new(prob: f32) -> Box<NoiseGenerator> {
+    pub fn new(prob: f32) -> Box<NoiseGenerator<D>> {
         Box::new(NoiseGenerator {
             prob,
+            phantom: PhantomData,
         })
     }
 
     /// Create uniform noise (Probablity 0.5)
-    pub fn uniform() -> Box<NoiseGenerator> {
+    pub fn uniform() -> Box<NoiseGenerator<D>> {
         Box::new(NoiseGenerator {
             prob: 0.5,
+            phantom: PhantomData,
         })
     }
 
     /// Generate map
-    fn build(&self, map: &Map, rng: &mut StdRng) -> Map {
+    fn build(&self, map: &Map<D>, rng: &mut StdRng) -> Map<D> {
         let mut new_map = map.clone();
         let p = (self.prob * 100.0) as u32;
         for y in 1..new_map.height-1 {
diff --git a/src/filter/rooms_corridors_nearest.rs b/src/filter/rooms_corridors_nearest.rs
index 7bbe717..74b44c9 100644
--- a/src/filter/rooms_corridors_nearest.rs
+++ b/src/filter/rooms_corridors_nearest.rs
@@ -1,26 +1,32 @@
 //! Connect nearest rooms on the map with corridors
 //! 
 use rand::prelude::StdRng;
+use crate::BuilderData;
 use crate::MapFilter;
 use crate::Map;
 use std::collections::HashSet;
+use std::marker::PhantomData;
 
 
-pub struct NearestCorridors {}
+pub struct NearestCorridors<D: BuilderData> {
+    phantom: PhantomData<D>,
+}
 
-impl MapFilter for NearestCorridors {
-    fn modify_map(&self, _: &mut StdRng, map: &Map)  -> Map {
+impl<D: BuilderData> MapFilter<D> for NearestCorridors<D> {
+    fn modify_map(&self, _: &mut StdRng, map: &Map<D>)  -> Map<D> {
         self.corridors(map)
     }
 }
 
-impl NearestCorridors {
+impl<D: BuilderData> NearestCorridors<D> {
 
-    pub fn new() -> Box<NearestCorridors> {
-        Box::new(NearestCorridors{})
+    pub fn new() -> Box<NearestCorridors<D>> {
+        Box::new(NearestCorridors {
+            phantom: PhantomData,
+        })
     }
 
-    fn corridors(&self, map: &Map) -> Map {
+    fn corridors(&self, map: &Map<D>) -> Map<D> {
         let mut new_map = map.clone();
 
         let mut connected : HashSet<usize> = HashSet::new();
diff --git a/src/filter/simple_rooms.rs b/src/filter/simple_rooms.rs
index 4335547..73000f7 100644
--- a/src/filter/simple_rooms.rs
+++ b/src/filter/simple_rooms.rs
@@ -6,11 +6,11 @@
 //! Example generator usage:
 //! ```
 //! use rand::prelude::*;
-//! use mapgen::{MapFilter, Map};
+//! use mapgen::{MapFilter, Map, NoData};
 //! use mapgen::filter::SimpleRooms;
 //! 
 //! let mut rng = StdRng::seed_from_u64(100);
-//! let gen = SimpleRooms::new();
+//! let gen = SimpleRooms::<NoData>::new();
 //! let map = gen.modify_map(&mut rng, &Map::new(80, 50));
 //! 
 //! assert_eq!(map.width, 80);
@@ -18,36 +18,41 @@
 //! ```
 //! 
 
+use std::marker::PhantomData;
+
 use rand::prelude::*;
+use crate::BuilderData;
 use crate::MapFilter;
 use crate::geometry::Rect;
 use crate::random::Rng;
 use crate::Map;
 
 
-pub struct SimpleRooms {
+pub struct SimpleRooms<D: BuilderData> {
     max_rooms: usize,
     min_room_size: usize,
     max_room_size: usize,
+    phantom: PhantomData<D>,
 }
 
-impl MapFilter for SimpleRooms {
-    fn modify_map(&self, rng: &mut StdRng, map: &Map)  -> Map {
+impl<D: BuilderData> MapFilter<D> for SimpleRooms<D> {
+    fn modify_map(&self, rng: &mut StdRng, map: &Map<D>)  -> Map<D> {
         self.build_rooms(map, rng)
     }
 }
 
 
-impl SimpleRooms {
-    pub fn new() -> Box<SimpleRooms> {
+impl<D: BuilderData> SimpleRooms<D> {
+    pub fn new() -> Box<SimpleRooms<D>> {
         Box::new(SimpleRooms{
             max_rooms: 30,
             min_room_size: 6,
-            max_room_size: 10
+            max_room_size: 10,
+            phantom: PhantomData,
         })
     }
 
-    fn build_rooms(&self, map: &Map, rng : &mut StdRng) -> Map {
+    fn build_rooms(&self, map: &Map<D>, rng : &mut StdRng) -> Map<D> {
         let mut new_map = map.clone();
 
         // Create room dimensions
diff --git a/src/filter/starting_point.rs b/src/filter/starting_point.rs
index bed4f69..7f6c5d1 100644
--- a/src/filter/starting_point.rs
+++ b/src/filter/starting_point.rs
@@ -6,12 +6,12 @@
 //! Example modifier usage:
 //! ```
 //! use rand::prelude::*;
-//! use mapgen::{MapFilter, Map, Tile};
+//! use mapgen::{MapFilter, Map, NoData, Tile};
 //! use mapgen::filter::starting_point::{AreaStartingPosition, XStart, YStart};
 //! use mapgen::geometry::Point;
 //! 
 //! let mut rng = StdRng::seed_from_u64(100);
-//! let mut map = Map::new(80, 50);
+//! let mut map = Map::<NoData>::new(80, 50);
 //! map.set_tile(10, 10, Tile::floor());
 //! let modifier = AreaStartingPosition::new(XStart::LEFT, YStart::TOP);
 //! let new_map = modifier.modify_map(&mut rng, &map);
@@ -20,7 +20,10 @@
 //! ```
 //! 
 
+use std::marker::PhantomData;
+
 use rand::prelude::StdRng;
+use crate::BuilderData;
 use crate::MapFilter;
 use crate::geometry::Point;
 use crate::Map;
@@ -33,26 +36,28 @@ pub enum XStart { LEFT, CENTER, RIGHT }
 pub enum YStart { TOP, CENTER, BOTTOM }
 
 /// Add starting position to the map
-pub struct AreaStartingPosition {
+pub struct AreaStartingPosition<D: BuilderData> {
     x : XStart, 
-    y : YStart
+    y : YStart,
+    phantom: PhantomData<D>,
 }
 
-impl MapFilter for AreaStartingPosition {
-    fn modify_map(&self, _: &mut StdRng, map: &Map)  -> Map {
+impl<D: BuilderData> MapFilter<D> for AreaStartingPosition<D> {
+    fn modify_map(&self, _: &mut StdRng, map: &Map<D>)  -> Map<D> {
         self.build(map)
     }
 }
 
-impl AreaStartingPosition {
+impl<D: BuilderData> AreaStartingPosition<D> {
     /// Create new modifier with given region
-    pub fn new(x : XStart, y : YStart) -> Box<AreaStartingPosition> {
+    pub fn new(x : XStart, y : YStart) -> Box<AreaStartingPosition<D>> {
         Box::new(AreaStartingPosition{
-            x, y
+            x, y,
+            phantom: PhantomData,
         })
     }
 
-    fn build(&self, map : &Map) -> Map {
+    fn build(&self, map : &Map<D>) -> Map<D> {
         let seed_x = match self.x {
             XStart::LEFT => 1,
             XStart::CENTER => map.width / 2,
@@ -101,7 +106,7 @@ mod tests {
     use super::*;
     use super::MapFilter;
     use crate::geometry::Point;
-    use crate::map::Map;
+    use crate::map::{Map, NoData};
 
     #[test]
     fn test_exit() {
@@ -111,7 +116,7 @@ mod tests {
         #  # #   #
         ##########
         ";
-        let mut map = Map::from_string(map_str);
+        let mut map = Map::<NoData>::from_string(map_str);
         map.starting_point = Some(Point::new(9, 2));
 
         let modifier = AreaStartingPosition::new(XStart::CENTER, YStart::TOP);
diff --git a/src/filter/voronoi.rs b/src/filter/voronoi.rs
index adb650a..1a1b647 100644
--- a/src/filter/voronoi.rs
+++ b/src/filter/voronoi.rs
@@ -1,11 +1,11 @@
 //! Example generator usage:
 //! ```
 //! use rand::prelude::*;
-//! use mapgen::{Map, MapFilter};
+//! use mapgen::{Map, MapFilter, NoData};
 //! use mapgen::filter::VoronoiHive;
 //! 
 //! let mut rng = StdRng::seed_from_u64(100);
-//! let gen = VoronoiHive::new();
+//! let gen = VoronoiHive::<NoData>::new();
 //! let map = gen.modify_map(&mut rng, &Map::new(80, 50));
 //! 
 //! assert_eq!(map.width, 80);
@@ -13,34 +13,38 @@
 //! ```
 //! 
 
+use std::marker::PhantomData;
+
 use rand::prelude::*;
 use crate::MapFilter;
 use crate::{
-    map::{Map, Tile},
+    map::{BuilderData, Map, Tile},
     random::Rng,
     geometry::Point,
 };
 
 
-pub struct VoronoiHive {
+pub struct VoronoiHive<D: BuilderData> {
     n_seeds: usize,
+    phantom: PhantomData<D>,
 }
 
 
-impl MapFilter for VoronoiHive {
-    fn modify_map(&self, rng: &mut StdRng, map: &Map)  -> Map {
+impl<D: BuilderData> MapFilter<D> for VoronoiHive<D> {
+    fn modify_map(&self, rng: &mut StdRng, map: &Map<D>)  -> Map<D> {
         self.build(rng, map)
     }
 }
 
-impl VoronoiHive {
-    pub fn new() -> Box<VoronoiHive> {
+impl<D: BuilderData> VoronoiHive<D> {
+    pub fn new() -> Box<VoronoiHive<D>> {
         Box::new(VoronoiHive{
             n_seeds: 64,
+            phantom: PhantomData,
         })
     }
 
-    fn build(&self, rng: &mut StdRng, map: &Map) -> Map {
+    fn build(&self, rng: &mut StdRng, map: &Map<D>) -> Map<D> {
         let mut new_map = map.clone();
         let seeds = self.generate_seeds(rng, map.width, map.height);
 
diff --git a/src/lib.rs b/src/lib.rs
index f0ab09e..44f3066 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -8,7 +8,7 @@
 //! 
 //! Example
 //! ```
-//! use mapgen::{MapFilter, MapBuilder, Map, Tile};
+//! use mapgen::{MapFilter, MapBuilder, Map, NoData, Tile};
 //! use mapgen::filter::{
 //!     NoiseGenerator,
 //!     CellularAutomata,
@@ -16,7 +16,7 @@
 //! };
 //! use mapgen::geometry::Point;
 //! 
-//! let map = MapBuilder::new(80, 50)
+//! let map = MapBuilder::<NoData>::new(80, 50)
 //!             .with(NoiseGenerator::uniform())
 //!             .with(CellularAutomata::new())
 //!             .with(AreaStartingPosition::new(XStart::CENTER, YStart::CENTER))
@@ -33,7 +33,7 @@ pub mod geometry;
 pub mod map;
 pub mod metric;
 
-pub use map::{Map, Symmetry, Tile};
+pub use map::{BuilderData, Map, NoData, Symmetry, Tile};
 pub use filter::*;
 
 pub (crate) mod dijkstra;
@@ -45,20 +45,20 @@ use rand::prelude::*;
 
 /// Trait which should be implemented by map modifier. 
 /// Modifier takes initiall map and apply changes to it.
-pub trait MapFilter {
-    fn modify_map(&self, rng: &mut StdRng, map: &Map) -> Map;
+pub trait MapFilter<D: BuilderData> {
+    fn modify_map(&self, rng: &mut StdRng, map: &Map<D>) -> Map<D>;
 }
 
 /// Used to chain MapBuilder and MapModifiers to create the final map.
-pub struct MapBuilder {
+pub struct MapBuilder<D> {
     width: usize,
     height: usize,
-    modifiers: Vec<Box<dyn MapFilter>>,
+    modifiers: Vec<Box<dyn MapFilter<D>>>,
 }
 
-impl MapBuilder {
+impl<D: BuilderData> MapBuilder<D> {
     /// Create Map Builder with initial map generator
-    pub fn new(width: usize, height: usize) -> MapBuilder {
+    pub fn new(width: usize, height: usize) -> MapBuilder<D> {
         MapBuilder { 
             width,
             height,
@@ -66,20 +66,20 @@ impl MapBuilder {
         }
     }
 
-    pub fn with(&mut self, modifier : Box<dyn MapFilter>) -> &mut MapBuilder {
+    pub fn with(&mut self, modifier : Box<dyn MapFilter<D>>) -> &mut MapBuilder<D> {
         self.modifiers.push(modifier);
         self
     }
 
     /// Build map using random number seeded with system time
-    pub fn build(&mut self) -> Map {
+    pub fn build(&mut self) -> Map<D> {
         let system_time = SystemTime::now().duration_since(UNIX_EPOCH).expect("Can't access system time");
         let mut rng = StdRng::seed_from_u64(system_time.as_millis() as u64);
         self.build_with_rng(&mut rng)
     }
 
     /// Build map using provided random number generator
-    pub fn build_with_rng(&mut self, rng: &mut StdRng) -> Map {
+    pub fn build_with_rng(&mut self, rng: &mut StdRng) -> Map<D> {
         let mut map = Map::new(self.width, self.height);
         
         // Build additional layers in turn
@@ -97,6 +97,8 @@ impl MapBuilder {
 /// ------------------------------------------------------------------------------------------------
 #[cfg(test)]
 mod tests {
+    use crate::map::NoData;
+
     use super::*;
     use filter::{
         CellularAutomata,
@@ -106,7 +108,7 @@ mod tests {
 
     #[test]
     fn test_ca_map() {
-        let map = MapBuilder::new(80, 50)
+        let map = MapBuilder::<NoData>::new(80, 50)
             .with(NoiseGenerator::new(0.55))
             .with(CellularAutomata::new())
             .with(AreaStartingPosition::new(XStart::CENTER, YStart::CENTER))
diff --git a/src/map.rs b/src/map.rs
index 8339ae1..36551f9 100644
--- a/src/map.rs
+++ b/src/map.rs
@@ -21,9 +21,18 @@ pub struct Tile {
 pub enum Symmetry { None, Horizontal, Vertical, Both }
 
 
+/// Arbitrary data associated with each map
+pub trait BuilderData: Clone + Default {}
+
+/// No build data
+#[derive(Clone, Debug, Default)]
+pub struct NoData;
+
+impl BuilderData for NoData {}
+
 /// Map data
 #[derive(Default, Clone)]
-pub struct Map {
+pub struct Map<D> {
     pub tiles : Vec<Tile>,
     pub width : usize,
     pub height : usize,
@@ -31,6 +40,7 @@ pub struct Map {
     pub exit_point: Option<Point>,
     pub rooms: Vec<Rect>,
     pub corridors: Vec<Vec<Point>>,
+    pub data: D,
 }
 
 impl Tile {
@@ -59,10 +69,10 @@ impl Tile {
     }
 }
 
-impl Map {
+impl<D: BuilderData> Map<D> {
 
     /// Generates an empty map, consisting entirely of solid walls
-    pub fn new(width: usize, height: usize) -> Map {
+    pub fn new(width: usize, height: usize) -> Map<D> {
         let map_tile_count = width*height;
         Map{
             tiles : vec![Tile::wall(); map_tile_count],
@@ -71,12 +81,13 @@ impl Map {
             starting_point: None,
             exit_point: None,
             rooms: Vec::new(),
-            corridors: Vec::new()
+            corridors: Vec::new(),
+            data: Default::default()
         }
     }
 
     /// Create map from given string
-    pub fn from_string(map_string: &str) -> Map {
+    pub fn from_string(map_string: &str) -> Map<D> {
         let lines: Vec<&str> = map_string.split("\n")
             .map(|l| l.trim())
             .filter(|l| l.len() > 0)
@@ -235,7 +246,7 @@ impl Map {
     }
 }
 
-impl fmt::Display for Map {
+impl<D: BuilderData> fmt::Display for Map<D> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         for y in 0..self.height {
             let bytes: Vec<u8> = (0..self.width)
@@ -257,7 +268,7 @@ mod tests {
 
     #[test]
     fn test_new_map() {
-        let map = Map::new(10, 10);
+        let map = Map::<NoData>::new(10, 10);
         for i in 0..10 {
             for j in 0..10 {
                 assert!(map.at(i, j).is_blocked);
@@ -272,7 +283,7 @@ mod tests {
         #        #
         ##########
         ";
-        let map = Map::from_string(map_str);
+        let map = Map::<NoData>::from_string(map_str);
 
         assert_eq!(map.width, 10);
         assert_eq!(map.height, 3);
@@ -295,7 +306,7 @@ mod tests {
         #        #
         ##########
         ";
-        let map = Map::from_string(map_str);
+        let map = Map::<NoData>::from_string(map_str);
         let exists = map.get_available_exits(1, 1);
         let expected_exists = vec![(2, 1, 1.0), (1, 2, 1.0), (2, 2, 1.45)];
         assert_eq!(exists, expected_exists);
@@ -303,7 +314,7 @@ mod tests {
 
         #[test]
     fn test_create_room() {
-        let mut map = Map::new(5, 5);
+        let mut map = Map::<NoData>::new(5, 5);
         map.add_room(Rect::new(1, 1, 3, 3));
         for x in 0..map.width {
             for y in 0..map.height {
@@ -323,13 +334,13 @@ mod tests {
         #    #   #
         ##########
         ";
-        let mut map = Map::from_string(map_str);
+        let mut map = Map::<NoData>::from_string(map_str);
         let expected_map_str = "
         ##########
         #        #
         ##########
         ";
-        let expected_map = Map::from_string(expected_map_str);
+        let expected_map = Map::<NoData>::from_string(expected_map_str);
 
         map.add_corridor(Point::new(1, 1), Point::new(8, 1));
 
@@ -344,7 +355,7 @@ mod tests {
         #    #   #
         ##########
         ";
-        let map = Map::from_string(map_str);
+        let map = Map::<NoData>::from_string(map_str);
         let exists = map.get_available_exits(0, 0);
 
         assert_eq!(exists.len(), 1);
diff --git a/src/metric.rs b/src/metric.rs
index 4736fcb..9dbe0fa 100644
--- a/src/metric.rs
+++ b/src/metric.rs
@@ -4,6 +4,7 @@
 //! and the provide generator score as an average.
 //! 
 
+use super::BuilderData;
 use super::map::Map;
 use super::dijkstra::DijkstraMap;
 
@@ -11,7 +12,7 @@ use super::dijkstra::DijkstraMap;
 /// This metric calculates the percentage of walkable cells (Floor).
 /// If this number is very low (like < 10%) then it means that the map 
 /// is probably to degenerated and shouldn't be used
-pub fn density(map: &Map) -> f32 {
+pub fn density<D>(map: &Map<D>) -> f32 {
     let floor_count = map.tiles.iter()
         .filter(|&t| t.is_walkable())
         .count();
@@ -22,7 +23,7 @@ pub fn density(map: &Map) -> f32 {
 /// Calculate the length of the shortes path from the starting point
 /// to the exit.
 /// If this path is very short, then the map is probably degenerated.
-pub fn path_length(map: &Map) -> f32 {
+pub fn path_length<D: BuilderData>(map: &Map<D>) -> f32 {
     if map.starting_point.is_none() {
         return 0.0
     }
@@ -43,12 +44,12 @@ pub fn path_length(map: &Map) -> f32 {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::geometry::Point;
+    use crate::{geometry::Point, map::NoData};
 
 
     #[test]
     fn test_density_no_floor() {
-        let map = Map::new(10, 10);
+        let map = Map::<NoData>::new(10, 10);
         let score = density(&map);
         assert_eq!(score, 0.0);
     }
@@ -60,7 +61,7 @@ mod tests {
             #   ##   #
             ##########
             ";
-        let map = Map::from_string(map_str);
+        let map = Map::<NoData>::from_string(map_str);
         let score = density(&map);
         assert_eq!(score, 0.2);
     }
@@ -72,7 +73,7 @@ mod tests {
             #   ##   #
             ##########
             ";
-        let map = Map::from_string(map_str);
+        let map = Map::<NoData>::from_string(map_str);
         let score = path_length(&map);
         assert_eq!(score, 0.0);
     }
@@ -85,7 +86,7 @@ mod tests {
             #        #
             ##########
             ";
-        let mut map = Map::from_string(map_str);
+        let mut map = Map::<NoData>::from_string(map_str);
         map.starting_point = Some(Point::new(1,1));
         map.exit_point = Some(Point::new(8,1));