Cleanup documentation

README.md

@@ -2,37 +2,43 @@
 
 # HexTree
 
-hextree provides tree structures that represent geographic regions
-with [H3 cell]s.
+HexTree provides tree structures for efficiently representing geographic
+regions using [H3 cell]s. It takes advantage of H3's hierarchical structure
+to automatically compact large regions and provide fast spatial queries.
 
 The primary structures are:
 
 - [**HexTreeMap**]: an H3 cell-to-value map.
-- [**HexTreeSet**]: an H3 cell set for hit-testing.
+- [**HexTreeSet**]: an H3 cell set for spatial containment testing.
 
 You can think of `HexTreeMap` vs. `HexTreeSet` as [`HashMap`] vs. [`HashSet`].
 
 ## How is this different from `HashMap<H3Cell, V>`?
 
-The key feature of a hextree is that its keys (H3 cells) are
-hierarchical. For instance, if you previously inserted an entry for a
-low-res cell, but later query for a higher-res child cell, the tree
-returns the value for the lower res cell. Additionally, with
-[compaction], trees can automatically coalesce adjacent high-res cells
-into their parent cell. For very large regions, the compaction process
-_can_ continue to lowest resolution cells (res-0), possibly removing
-millions of redundant cells from the tree. For example, a set of
-4,795,661 res-7 cells representing North America coalesces [into a
-42,383 element `HexTreeSet`][us915].
-
-A hextree's internal structure exactly matches the semantics of an [H3
-cell]. The root of the tree has 122 resolution-0 nodes, followed by 15
-levels of 7-ary nodes. The level of an occupied node, or leaf node, is
-the same as its corresponding H3 cell resolution.
+HexTree leverages H3's hierarchical cell structure in two key ways:
+
+**Hierarchical Queries**: When you query for a cell, the tree returns
+a value even if only a parent cell was inserted. For instance, if you
+insert a low-res cell but later query for a higher-res child cell, the
+tree returns the value from the parent.
+
+**Automatic Compaction**: With [compaction], the tree can automatically
+coalesce 7 adjacent child cells into their parent cell, dramatically
+reducing memory usage. For very large regions, compaction can continue
+recursively to the lowest resolution cells (res-0), possibly removing
+millions of redundant cells. For example, 4,795,661 res-7 cells
+representing North America compact [into just 42,383 elements][us915].
+
+The internal structure mirrors H3's hierarchy: the root contains 122
+resolution-0 base cells, with each level below being a 7-ary tree
+(matching H3's 7 possible child cells per parent). The tree supports
+up to 15 levels of resolution, where the depth of a leaf node corresponds
+to its H3 cell resolution.
 
 ## Features
 
 * **`serde`**: support for serialization via [serde].
+* **`disktree`**: on-disk memory-mapped storage for large trees (enables `serde`, `byteorder`, and `memmap`).
 
 ## License
 

src/cell.rs

@@ -1,14 +1,14 @@
-//! This has two different types representing H3 indices is slightly
+//! This has two different types representing H3 indices in slightly
 //! different ways, [Index] & [Cell]. Index is lower level and allows
-//! you create invalid H3 indices. Cell is higher level and enforces
+//! you to create invalid H3 indices. Cell is higher level and enforces
 //! invariants.
 
 use crate::{Error, Result};
 use std::{convert::TryFrom, fmt};
 
 /// A low-level type for H3 [index manipulation].
 ///
-/// Node that all setters take consume `self` and return a new
+/// Note that all setters consume `self` and return a new
 /// `Index`.
 ///
 /// [index manipulation]: https://observablehq.com/@nrabinowitz/h3-index-bit-layout?collection=@nrabinowitz/h3
@@ -112,7 +112,7 @@ impl Index {
         }
     }
 
-    /// Consumes `self` and returns a new Index with it's resolution
+    /// Consumes `self` and returns a new Index with its resolution
     /// `res` digit set to `digit`.
     ///
     /// This function does not check `res` nor `digit` for validity
@@ -129,7 +129,10 @@ impl Index {
     }
 }
 
-/// [HexTreeMap][crate::HexTreeMap]'s key type.
+/// A validated H3 cell index.
+///
+/// This is the key type for [HexTreeMap][crate::HexTreeMap]. A `Cell`
+/// is guaranteed to be a valid H3 cell (mode 1 index).
 #[derive(Clone, Copy, Eq, Hash, PartialEq)]
 #[cfg_attr(
     feature = "serde",
@@ -153,7 +156,7 @@ impl Cell {
         if
         // reserved must be 0
         !idx.reserved() &&
-        // we only care about mode 1 (cell) indicies
+        // we only care about mode 1 (cell) indices
         idx.mode() == 1 &&
         // there are only 122 base cells
         idx.base() < 122
@@ -172,8 +175,9 @@ impl Cell {
 
     /// Returns this cell's parent at the specified resolution.
     ///
-    /// Returns Some if `res` is less-than or equal-to this cell's
-    /// resolution, otherwise returns None.
+    /// Returns `Some` if `res` is less than or equal to this cell's
+    /// resolution. Returns `None` if `res` is greater than this cell's
+    /// resolution (you cannot get a higher-resolution parent).
     #[inline]
     pub const fn to_parent(&self, res: u8) -> Option<Self> {
         match self.res() {
@@ -203,12 +207,12 @@ impl Cell {
         Index(self.0).res()
     }
 
-    /// Returns true if `self` is related to `other`.
+    /// Returns `true` if this cell is related to another cell.
     ///
-    /// "Related" can be any of the following:
-    /// - `self` == `other`
-    /// - `self` is a parent cell of `other`
-    /// - `other` is a parent cell of `self`
+    /// Two cells are related if they share a parent-child relationship:
+    /// - `self` and `other` are the same cell, or
+    /// - `self` is an ancestor (parent, grandparent, etc.) of `other`, or
+    /// - `other` is an ancestor of `self`
     #[inline]
     pub fn is_related_to(&self, other: &Self) -> bool {
         let common_res = std::cmp::min(self.res(), other.res());
@@ -238,7 +242,7 @@ impl TryFrom<i64> for Cell {
     }
 }
 
-/// A type for building up Cells in an iterative matter when
+/// A type for building up Cells in an iterative manner when
 /// tree-walking.
 pub(crate) struct CellStack(Option<Cell>);
 
@@ -282,7 +286,7 @@ impl CellStack {
         }
     }
 
-    /// If self currency contains a cell, this replaces the digit at
+    /// If self currently contains a cell, this replaces the digit at
     /// its current res and returns what was there. If self is empty,
     /// nothing is replaced and None is returned.
     pub fn swap(&mut self, digit: u8) -> Option<u8> {

src/compaction.rs

@@ -1,21 +1,27 @@
-//! User pluggable compaction.
+//! User-pluggable compaction strategies.
+//!
+//! Compaction allows the tree to automatically coalesce child cells into
+//! their parent when certain conditions are met, reducing memory usage
+//! and improving query performance.
 
 use crate::Cell;
 
-/// A user provided compactor.
+/// A user-provided compactor.
 ///
-/// The compactor trait allows you customize compaction behavior after
+/// The compactor trait allows you to customize compaction behavior after
 /// calling `insert` on a tree.
 pub trait Compactor<V> {
     /// Called after every insert into a non-leaf node.
     ///
-    /// Given an intermediate (not-leaf) node's cell and up to 7
+    /// Given an intermediate (non-leaf) node's cell and up to 7
     /// children, you can choose to leave the node alone by returning
-    /// `None`, or turn it into a leaf-node by return `Some(value)`.
+    /// `None`, or turn it into a leaf node by returning `Some(value)`.
     fn compact(&mut self, cell: Cell, children: [Option<&V>; 7]) -> Option<V>;
 }
 
-/// Does not perform any compaction.
+/// A compactor that performs no compaction.
+///
+/// This is the default compactor and leaves all inserted cells as-is.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct NullCompactor;
@@ -26,7 +32,11 @@ impl<V> Compactor<V> for NullCompactor {
     }
 }
 
-/// Compacts when all children are complete.
+/// A compactor that coalesces nodes when all 7 children are present.
+///
+/// This is typically used with `HexTreeSet` (where values are `()`).
+/// When all 7 children of a node are complete, they are replaced with
+/// a single parent cell.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct SetCompactor;
@@ -41,7 +51,11 @@ impl Compactor<()> for SetCompactor {
     }
 }
 
-/// Compacts when all children are complete and have the same value.
+/// A compactor that coalesces nodes when all 7 children have equal values.
+///
+/// When all 7 children of a node are present and have the same value,
+/// they are replaced with a single parent cell containing that value.
+/// This is useful for maps where large contiguous regions share the same value.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct EqCompactor;

src/disktree/mod.rs

@@ -1,4 +1,8 @@
-//! An on-disk hextree.
+//! On-disk memory-mapped storage for HexTree.
+//!
+//! DiskTree provides a serialized, memory-mapped representation of a HexTreeMap,
+//! allowing you to store and query very large trees without loading them entirely
+//! into memory.
 
 #[cfg(not(target_pointer_width = "64"))]
 compile_warning!("disktree may silently fail on non-64bit systems");
@@ -36,7 +40,7 @@ mod tests {
         }
 
         // Construct map with a compactor that automatically combines
-        // cells with the same save value.
+        // cells with the same value.
         let mut monaco = HexTreeMap::with_compactor(EqCompactor);
 
         // Now extend the map with cells and a region value.
@@ -190,7 +194,7 @@ mod tests {
         }
 
         // Construct map with a compactor that automatically combines
-        // cells with the same save value.
+        // cells with the same value.
         let mut monaco = HexTreeMap::new();
 
         // Now extend the map with cells and a region value.
@@ -204,7 +208,7 @@ mod tests {
             .unwrap();
         let monaco_disktree = DiskTreeMap::open(path).unwrap();
 
-        // Create the iterator with the user-defined deserialzer.
+        // Create the iterator with the user-defined deserializer.
         let disktree_iter = monaco_disktree.iter().unwrap();
         let start = std::time::Instant::now();
         let mut disktree_collection = Vec::new();
@@ -294,7 +298,7 @@ mod tests {
             assert_eq!(
                 leaf_vec.len(),
                 1,
-                "Iterator must have extactly one element for a leaf"
+                "Iterator must have exactly one element for a leaf"
             );
             assert_eq!(hextree_leaf, leaf_vec[0].0);
         }

src/disktree/tree.rs

@@ -16,7 +16,10 @@ use std::{
 pub(crate) const HDR_MAGIC: &[u8] = b"hextree\0";
 pub(crate) const HDR_SZ: usize = HDR_MAGIC.len() + 1;
 
-/// An on-disk hextree map.
+/// A memory-mapped, on-disk HexTreeMap.
+///
+/// This structure provides read-only access to a HexTreeMap that has
+/// been serialized to disk.
 pub struct DiskTreeMap(pub(crate) Box<dyn AsRef<[u8]> + Send + Sync + 'static>);
 
 impl DiskTreeMap {

src/hex_tree_map.rs

@@ -42,7 +42,7 @@ use std::{cmp::PartialEq, iter::FromIterator};
 /// }
 ///
 /// // Construct map with a compactor that automatically combines
-/// // cells with the same save value.
+/// // cells with the same value.
 /// let mut monaco = HexTreeMap::with_compactor(EqCompactor);
 ///
 /// // Now extend the map with cells and a region value.
@@ -66,7 +66,7 @@ use std::{cmp::PartialEq, iter::FromIterator};
 pub struct HexTreeMap<V, C = NullCompactor> {
     /// All h3 0 base cell indices in the tree
     pub(crate) nodes: Box<[Option<Box<Node<V>>>]>,
-    /// User-provided compator. Defaults to the null compactor.
+    /// User-provided compactor. Defaults to the null compactor.
     compactor: C,
 }
 
@@ -121,7 +121,7 @@ impl<V, C> HexTreeMap<V, C> {
     /// `self`.
     ///
     /// This method is useful if you want to use one compaction
-    /// strategy for creating an initial, then another one for updates
+    /// strategy for creating an initial tree, then another one for updates
     /// later.
     pub fn replace_compactor<NewC>(self, new_compactor: NewC) -> HexTreeMap<V, NewC> {
         HexTreeMap {
@@ -130,12 +130,11 @@ impl<V, C> HexTreeMap<V, C> {
         }
     }
 
-    /// Returns the number of H3 cells in the set.
+    /// Returns the number of H3 cells in the map.
     ///
-    /// This method only considers complete, or leaf, cells in the
-    /// set. Due to automatic compaction, this number may be
-    /// significantly smaller than the number of source cells used to
-    /// create the set.
+    /// This method only counts leaf cells (complete entries) in the
+    /// map. Due to automatic compaction, this number may be
+    /// significantly smaller than the number of cells originally inserted.
     pub fn len(&self) -> usize {
         self.nodes.iter().flatten().map(|node| node.len()).sum()
     }
@@ -145,17 +144,15 @@ impl<V, C> HexTreeMap<V, C> {
         self.len() == 0
     }
 
-    /// Returns `true` if the set fully contains `cell`.
+    /// Returns `true` if the map fully contains `cell`.
     ///
-    /// This method will return `true` if any of the following are
-    /// true:
+    /// This method returns `true` if any of the following are true:
     ///
-    /// 1. There was an earlier [insert][Self::insert] call with
-    ///    precisely this target cell.
-    /// 2. Several previously inserted cells coalesced into
-    ///    precisely this target cell.
-    /// 3. The set contains a complete (leaf) parent of this target
-    ///    cell due to 1 or 2.
+    /// 1. This exact cell was previously inserted.
+    /// 2. Several previously inserted cells were compacted into
+    ///    this cell as their parent.
+    /// 3. The map contains a parent of this cell (due to 1 or 2),
+    ///    meaning this cell inherits its parent's value.
     pub fn contains(&self, cell: Cell) -> bool {
         let base_cell = cell.base();
         match self.nodes[base_cell as usize].as_ref() {
@@ -167,11 +164,11 @@ impl<V, C> HexTreeMap<V, C> {
         }
     }
 
-    /// Returns a reference to the value corresponding to the given
-    /// target cell or one of its parents.
+    /// Returns a reference to the value for the given cell or its nearest parent.
     ///
-    /// Note that this method also returns a Cell, which may be a
-    /// parent of the target cell provided.
+    /// Returns `Some((cell, value))` where `cell` is either the queried cell
+    /// or a parent cell that contains it. Returns `None` if no matching cell
+    /// or parent is found.
     #[inline]
     pub fn get(&self, cell: Cell) -> Option<(Cell, &V)> {
         match self.get_raw(cell) {
@@ -192,11 +189,11 @@ impl<V, C> HexTreeMap<V, C> {
         }
     }
 
-    /// Returns a mutable reference to the value corresponding to the
-    /// given target cell or one of its parents.
+    /// Returns a mutable reference to the value for the given cell or its nearest parent.
     ///
-    /// Note that this method also returns a Cell, which may be a
-    /// parent of the target cell provided.
+    /// Returns `Some((cell, value))` where `cell` is either the queried cell
+    /// or a parent cell that contains it. Returns `None` if no matching cell
+    /// or parent is found.
     #[inline]
     pub fn get_mut(&mut self, cell: Cell) -> Option<(Cell, &mut V)> {
         match self.get_raw_mut(cell) {
@@ -242,7 +239,7 @@ impl<V, C> HexTreeMap<V, C> {
         crate::iteration::IterMut::new(&mut self.nodes, CellStack::new())
     }
 
-    /// An iterator visiting the specified cell or its children
+    /// An iterator visiting the specified cell or its children with
     /// references to the values.
     pub fn descendants(&self, cell: Cell) -> impl Iterator<Item = (Cell, &V)> {
         let base_cell = cell.base();

src/hex_tree_set.rs

@@ -2,7 +2,7 @@ use crate::{compaction::SetCompactor, Cell, HexTreeMap};
 use std::iter::FromIterator;
 
 /// A HexTreeSet is a structure for representing geographical regions
-/// and efficiently testing performing hit-tests on that region. Or,
+/// and efficiently performing hit-tests on that region. Or,
 /// in other words: I have a region defined; does it contain this
 /// point on earth?
 ///