diff --git a/src/bin/minedmap/main.rs b/src/bin/minedmap/main.rs
index 34aa985..8d3bbea 100644
--- a/src/bin/minedmap/main.rs
+++ b/src/bin/minedmap/main.rs
@@ -1,5 +1,6 @@
 mod common;
 mod metadata_writer;
+mod region_group;
 mod region_processor;
 mod tile_mipmapper;
 mod tile_renderer;
diff --git a/src/bin/minedmap/region_group.rs b/src/bin/minedmap/region_group.rs
new file mode 100644
index 0000000..0a12fd8
--- /dev/null
+++ b/src/bin/minedmap/region_group.rs
@@ -0,0 +1,80 @@
+use std::iter;
+
+use anyhow::Result;
+
+/// A generic array of 3x3 elements
+///
+/// A RegionGroup is used to store information about a 3x3 neighbourhood of
+/// regions.
+///
+/// The center element is always populated, while the 8 adjacent elements may be None.
+#[derive(Debug, Clone, Copy)]
+pub struct RegionGroup<T> {
+	center: T,
+	neighs: [Option<T>; 8],
+}
+
+impl<T> RegionGroup<T> {
+	pub fn new<F>(f: F) -> Result<Self>
+	where
+		F: Fn(i8, i8) -> Result<T>,
+	{
+		RegionGroup {
+			center: (0, 0),
+			neighs: [
+				Some((-1, -1)),
+				Some((-1, 0)),
+				Some((-1, 1)),
+				Some((0, -1)),
+				Some((0, 1)),
+				Some((1, -1)),
+				Some((1, 0)),
+				Some((1, 1)),
+			],
+		}
+		.try_map(|(x, z)| f(x, z))
+	}
+
+	pub fn center(&self) -> &T {
+		&self.center
+	}
+
+	pub fn get(&self, x: i8, z: i8) -> Option<&T> {
+		match (x, z) {
+			(0, 0) => Some(&self.center),
+			(-1, -1) => self.neighs[0].as_ref(),
+			(-1, 0) => self.neighs[1].as_ref(),
+			(-1, 1) => self.neighs[2].as_ref(),
+			(0, -1) => self.neighs[3].as_ref(),
+			(0, 1) => self.neighs[4].as_ref(),
+			(1, -1) => self.neighs[5].as_ref(),
+			(1, 0) => self.neighs[6].as_ref(),
+			(1, 1) => self.neighs[7].as_ref(),
+			_ => panic!("index out of bounds"),
+		}
+	}
+
+	pub fn map<U, F>(self, mut f: F) -> RegionGroup<U>
+	where
+		F: FnMut(T) -> U,
+	{
+		RegionGroup {
+			center: f(self.center),
+			neighs: self.neighs.map(|entry| entry.map(|v| f(v))),
+		}
+	}
+
+	pub fn try_map<U, F>(self, mut f: F) -> Result<RegionGroup<U>>
+	where
+		F: FnMut(T) -> Result<U>,
+	{
+		let RegionGroup { center, neighs } = self;
+		let center = f(center)?;
+		let neighs = neighs.map(|entry| entry.map(|value| f(value).ok()).flatten());
+		Ok(RegionGroup { center, neighs })
+	}
+
+	pub fn iter(&self) -> impl Iterator<Item = &T> {
+		iter::once(&self.center).chain(self.neighs.iter().filter_map(Option::as_ref))
+	}
+}