diff --git a/Sources/GISTools/GeoJson/BoundingBox.swift b/Sources/GISTools/GeoJson/BoundingBox.swift
index 07065d0..0843943 100644
--- a/Sources/GISTools/GeoJson/BoundingBox.swift
+++ b/Sources/GISTools/GeoJson/BoundingBox.swift
@@ -6,7 +6,6 @@ import Foundation
 /// A GeoJSON bounding box.
 public struct BoundingBox:
     GeoJsonReadable,
-    Projectable,
     CustomStringConvertible,
     Sendable
 {
@@ -42,7 +41,16 @@ public struct BoundingBox:
     }
 
     /// Create a bounding box from `coordinates` and an optional padding in kilometers.
-    public init?(coordinates: [Coordinate3D], paddingKilometers: Double = 0.0) {
+    @available(*, deprecated, renamed: "init(coordinates:padding:)", message: "Padding is now expressed in meters")
+    public init?(coordinates: [Coordinate3D], paddingKilometers: Double) {
+        self.init(coordinates: coordinates, padding: paddingKilometers * 1000.0)
+    }
+
+    /// Create a bounding box from `coordinates` and an optional padding.
+    ///
+    /// - Parameters:
+    ///    - padding: The padding, in meters
+    public init?(coordinates: [Coordinate3D], padding: CLLocationDistance = 0.0) {
         guard !coordinates.isEmpty else { return nil }
 
         self.projection = coordinates.first?.projection ?? .epsg4326
@@ -60,21 +68,21 @@ public struct BoundingBox:
             northEast.longitude = max(northEast.longitude, currentLocationLongitude)
         }
 
-        if paddingKilometers > 0.0 {
+        if padding > 0.0 {
             switch projection {
             case .epsg3857:
-                southWest.latitude -= paddingKilometers * 1000.0
-                northEast.latitude += paddingKilometers * 1000.0
-                southWest.longitude -= paddingKilometers * 1000.0
-                northEast.longitude += paddingKilometers * 1000.0
+                southWest.latitude -= padding
+                northEast.latitude += padding
+                southWest.longitude -= padding
+                northEast.longitude += padding
 
             case .epsg4326:
                 // Length of one minute at this latitude
-                let oneDegreeLongitudeDistanceInKilometers: Double = cos(southWest.latitude * Double.pi / 180.0) * 111.0
-                let oneDegreeLatitudeDistanceInKilometers = 111.0
+                let oneDegreeLatitudeDistance: CLLocationDistance = GISTool.earthCircumference / 360.0 // ~111 km
+                let oneDegreeLongitudeDistance: CLLocationDistance = cos(southWest.latitude * Double.pi / 180.0) * oneDegreeLatitudeDistance
 
-                let longitudeDistance: Double = (paddingKilometers / oneDegreeLongitudeDistanceInKilometers)
-                let latitudeDistance: Double = (paddingKilometers / oneDegreeLatitudeDistanceInKilometers)
+                let longitudeDistance: Double = (padding / oneDegreeLongitudeDistance)
+                let latitudeDistance: Double = (padding / oneDegreeLatitudeDistance)
 
                 southWest.latitude -= latitudeDistance
                 northEast.latitude += latitudeDistance
@@ -162,17 +170,34 @@ public struct BoundingBox:
     }
 
     /// Returns a copy of the receiver with some padding in kilometers.
+    @available(*, deprecated, renamed: "padded(_:)", message: "Padding is now expressed in meters")
     public func with(padding paddingKilometers: Double) -> BoundingBox {
         BoundingBox(
             coordinates: [southWest, northEast],
             paddingKilometers: paddingKilometers)!
     }
 
+    /// Returns a copy of the receiver with some padding horizontally and vertically.
+    ///
+    /// - Parameters:
+    ///    - padding: The padding, in meters
+    public func padded(_ padding: CLLocationDistance) -> BoundingBox {
+        BoundingBox(
+            coordinates: [southWest, northEast],
+            padding: padding)!
+    }
+
     /// Returns a copy of the receiver expanded by `degrees`.
+    @available(*, deprecated, renamed: "expanded(byDegrees:)", message: "Renamed to expaned(byDegrees:)")
     public func expand(_ degrees: CLLocationDegrees) -> BoundingBox {
+        expanded(byDegrees: degrees)
+    }
+
+    /// Returns a copy of the receiver expanded by `degrees` horizontally and vertically.
+    public func expanded(byDegrees degrees: CLLocationDegrees) -> BoundingBox {
         switch projection {
         case .epsg3857:
-            return projected(to: .epsg4326).expand(degrees).projected(to: .epsg3857)
+            return projected(to: .epsg4326).expanded(byDegrees: degrees).projected(to: .epsg3857)
 
         case .epsg4326:
             return BoundingBox(
@@ -185,19 +210,40 @@ public struct BoundingBox:
     }
 
     /// Returns a copy of the receiver expanded by `distance` diagonally.
+    @available(*, deprecated, renamed: "expanded(byDistance:)", message: "Renamed to expaned(byDistance:)")
     public func expand(distance: CLLocationDistance) -> BoundingBox {
+        expanded(byDistance: distance)
+    }
+
+    /// Returns a copy of the receiver expanded by `distance` diagonally.
+    ///
+    /// - Parameters:
+    ///    - distance: The distance from the receiver, in meters
+    public func expanded(byDistance distance: CLLocationDistance) -> BoundingBox {
         BoundingBox(
             southWest: southWest.destination(distance: distance, bearing: 225.0),
             northEast: northEast.destination(distance: distance, bearing: 45.0))
     }
 
     /// Returns a copy of the receiver that also includes `coordinate`.
+    @available(*, deprecated, renamed: "expanded(byIncluding:)", message: "Renamed to expanded(byIncluding:)")
     public func expand(including coordinate: Coordinate3D) -> BoundingBox {
+        expanded(byIncluding: coordinate)
+    }
+
+    /// Returns a copy of the receiver that also includes `coordinate`.
+    public func expanded(byIncluding coordinate: Coordinate3D) -> BoundingBox {
         BoundingBox(coordinates: [southWest, northEast, coordinate.projected(to: projection)])!
     }
 
     /// Returns a copy of the receiver that also includes the other `boundingBox`.
+    @available(*, deprecated, renamed: "expanded(byIncluding:)", message: "Renamed to expanded(byIncluding:)")
     public func expand(including boundingBox: BoundingBox) -> BoundingBox {
+        expanded(byIncluding: boundingBox)
+    }
+
+    /// Returns a copy of the receiver that also includes the other `boundingBox`.
+    public func expanded(byIncluding boundingBox: BoundingBox) -> BoundingBox {
         BoundingBox(coordinates: [
             southWest,
             northEast,
@@ -215,7 +261,7 @@ public struct BoundingBox:
 
 // MARK: - Projection
 
-extension BoundingBox {
+extension BoundingBox: Projectable {
 
     /// Reproject this bounding box.
     public func projected(to newProjection: Projection) -> BoundingBox {
@@ -234,20 +280,38 @@ extension BoundingBox {
 extension BoundingBox {
 
     /// Create a bounding box from `coordinates` and an optional padding in kilometers.
-    public init?(coordinates: [CLLocationCoordinate2D], paddingKilometers: Double = 0.0) {
+    @available(*, deprecated, renamed: "init(coordinates:padding:)", message: "Padding is now expressed in meters")
+    public init?(coordinates: [CLLocationCoordinate2D], paddingKilometers: Double) {
         self.init(coordinates: coordinates.map({ Coordinate3D($0) }), paddingKilometers: paddingKilometers)
     }
 
+    /// Create a bounding box from `coordinates` and an optional padding.
+    ///
+    /// - Parameters:
+    ///    - padding: The padding, in meters
+    public init?(coordinates: [CLLocationCoordinate2D], padding: Double = 0.0) {
+        self.init(coordinates: coordinates.map({ Coordinate3D($0) }), padding: padding)
+    }
+
     /// Create a bounding box from a south-west and north-east coordinate.
     public init(southWest: CLLocationCoordinate2D, northEast: CLLocationCoordinate2D) {
         self.init(southWest: Coordinate3D(southWest), northEast: Coordinate3D(northEast))
     }
 
     /// Create a bounding box from `locations` and an optional padding in kilometers.
+    @available(*, deprecated, renamed: "init(locations:padding:)", message: "Padding is now expressed in meters")
     public init?(locations: [CLLocation], paddingKilometers: Double = 0.0) {
         self.init(coordinates: locations.map({ Coordinate3D($0) }), paddingKilometers: paddingKilometers)
     }
 
+    /// Create a bounding box from `locations` and an optional padding.
+    ///
+    /// - Parameters:
+    ///    - padding: The padding, in meters
+    public init?(locations: [CLLocation], padding: Double = 0.0) {
+        self.init(coordinates: locations.map({ Coordinate3D($0) }), padding: padding)
+    }
+
     /// Create a bounding box from a south-west and north-east coordinate.
     public init(southWest: CLLocation, northEast: CLLocation) {
         self.init(southWest: Coordinate3D(southWest), northEast: Coordinate3D(northEast))
diff --git a/Sources/GISTools/GeoJson/Coordinate3D.swift b/Sources/GISTools/GeoJson/Coordinate3D.swift
index 4d70381..9cb8bf1 100644
--- a/Sources/GISTools/GeoJson/Coordinate3D.swift
+++ b/Sources/GISTools/GeoJson/Coordinate3D.swift
@@ -12,7 +12,6 @@ import Foundation
 /// A three dimensional coordinate (``latitude``/``y``, ``longitude``/``x``, ``altitude``/``z``)
 /// plus a generic value ``m``.
 public struct Coordinate3D:
-    Projectable,
     CustomStringConvertible,
     Sendable
 {
@@ -247,7 +246,7 @@ extension Coordinate3D {
 
 // MARK: - Projection
 
-extension Coordinate3D {
+extension Coordinate3D: Projectable {
 
     /// Reproject this coordinate.
     public func projected(to newProjection: Projection) -> Coordinate3D {
diff --git a/Sources/GISTools/GeoJson/Feature.swift b/Sources/GISTools/GeoJson/Feature.swift
index 5522194..f9f1f5c 100644
--- a/Sources/GISTools/GeoJson/Feature.swift
+++ b/Sources/GISTools/GeoJson/Feature.swift
@@ -4,7 +4,7 @@ import Foundation
 public struct Feature: GeoJson {
 
     /// A GeoJSON identifier that can either be a string or number.
-    public enum Identifier: Equatable, Hashable, CustomStringConvertible {
+    public enum Identifier: Equatable, Hashable, CustomStringConvertible, Sendable {
         case string(String)
         case int(Int)
         case double(Double)
@@ -61,11 +61,11 @@ public struct Feature: GeoJson {
     }
 
     /// Only 'Feature' objects may have properties.
-    public var properties: [String: Any]
+    public var properties: [String: Sendable]
 
     public var boundingBox: BoundingBox?
 
-    public var foreignMembers: [String: Any] = [:]
+    public var foreignMembers: [String: Sendable] = [:]
 
     /// Create a ``Feature`` from any ``GeoJsonGeometry`` object.
     public init(
diff --git a/Sources/GISTools/GeoJson/FeatureCollection.swift b/Sources/GISTools/GeoJson/FeatureCollection.swift
index 81645c5..c379320 100644
--- a/Sources/GISTools/GeoJson/FeatureCollection.swift
+++ b/Sources/GISTools/GeoJson/FeatureCollection.swift
@@ -23,7 +23,7 @@ public struct FeatureCollection:
 
     public var boundingBox: BoundingBox?
 
-    public var foreignMembers: [String: Any] = [:]
+    public var foreignMembers: [String: Sendable] = [:]
 
     public init() {
         self.features = []
diff --git a/Sources/GISTools/GeoJson/GeoJson.swift b/Sources/GISTools/GeoJson/GeoJson.swift
index c7be5ec..52c58c5 100644
--- a/Sources/GISTools/GeoJson/GeoJson.swift
+++ b/Sources/GISTools/GeoJson/GeoJson.swift
@@ -33,7 +33,8 @@ public protocol GeoJson:
     Projectable,
     ValidatableGeoJson,
     Codable,
-    CustomDebugStringConvertible
+    CustomDebugStringConvertible,
+    Sendable
 {
 
     /// GeoJSON object type.
@@ -45,7 +46,7 @@ public protocol GeoJson:
     /// Any foreign members, i.e. keys in the JSON that are
     /// not part of the GeoJSON standard.
     /// - important: `values` must be a valid JSON objects or serialization will fail.
-    var foreignMembers: [String: Any] { get set }
+    var foreignMembers: [String: Sendable] { get set }
 
     /// Try to initialize a GeoJSON object from any JSON and calculate a bounding box if necessary.
     ///
diff --git a/Sources/GISTools/GeoJson/GeometryCollection.swift b/Sources/GISTools/GeoJson/GeometryCollection.swift
index d8d401f..ae27909 100644
--- a/Sources/GISTools/GeoJson/GeometryCollection.swift
+++ b/Sources/GISTools/GeoJson/GeometryCollection.swift
@@ -20,7 +20,7 @@ public struct GeometryCollection: GeoJsonGeometry {
 
     public var boundingBox: BoundingBox?
 
-    public var foreignMembers: [String: Any] = [:]
+    public var foreignMembers: [String: Sendable] = [:]
 
     /// Initialize a GeometryCollection with a geometry object.
     public init(_ geometry: GeoJsonGeometry, calculateBoundingBox: Bool = false) {
diff --git a/Sources/GISTools/GeoJson/LineSegment.swift b/Sources/GISTools/GeoJson/LineSegment.swift
index 0491954..74fcb06 100644
--- a/Sources/GISTools/GeoJson/LineSegment.swift
+++ b/Sources/GISTools/GeoJson/LineSegment.swift
@@ -4,7 +4,7 @@ import CoreLocation
 import Foundation
 
 /// A `LineSegment` is a line with exactly two coordinates.
-public struct LineSegment: Projectable, Sendable {
+public struct LineSegment: Sendable {
 
     public var boundingBox: BoundingBox?
 
@@ -46,7 +46,7 @@ extension LineSegment {
 
 // MARK: - Projection
 
-extension LineSegment {
+extension LineSegment: Projectable {
 
     public func projected(to newProjection: Projection) -> LineSegment {
         guard newProjection != projection else { return self }
diff --git a/Sources/GISTools/GeoJson/LineString.swift b/Sources/GISTools/GeoJson/LineString.swift
index 7c5194f..8974cab 100644
--- a/Sources/GISTools/GeoJson/LineString.swift
+++ b/Sources/GISTools/GeoJson/LineString.swift
@@ -26,7 +26,7 @@ public struct LineString:
 
     public var boundingBox: BoundingBox?
 
-    public var foreignMembers: [String: Any] = [:]
+    public var foreignMembers: [String: Sendable] = [:]
 
     public var lineStrings: [LineString] {
         return [self]
diff --git a/Sources/GISTools/GeoJson/MultiLineString.swift b/Sources/GISTools/GeoJson/MultiLineString.swift
index 1a75cb9..e9f7855 100644
--- a/Sources/GISTools/GeoJson/MultiLineString.swift
+++ b/Sources/GISTools/GeoJson/MultiLineString.swift
@@ -26,7 +26,7 @@ public struct MultiLineString:
 
     public var boundingBox: BoundingBox?
 
-    public var foreignMembers: [String: Any] = [:]
+    public var foreignMembers: [String: Sendable] = [:]
 
     public var lineStrings: [LineString] {
         return coordinates.compactMap { LineString($0) }
diff --git a/Sources/GISTools/GeoJson/MultiPoint.swift b/Sources/GISTools/GeoJson/MultiPoint.swift
index e3a506a..102f2f2 100644
--- a/Sources/GISTools/GeoJson/MultiPoint.swift
+++ b/Sources/GISTools/GeoJson/MultiPoint.swift
@@ -26,7 +26,7 @@ public struct MultiPoint:
 
     public var boundingBox: BoundingBox?
 
-    public var foreignMembers: [String: Any] = [:]
+    public var foreignMembers: [String: Sendable] = [:]
 
     public var points: [Point] {
         return coordinates.map { Point($0) }
diff --git a/Sources/GISTools/GeoJson/MultiPolygon.swift b/Sources/GISTools/GeoJson/MultiPolygon.swift
index c3fd8ca..80baa26 100644
--- a/Sources/GISTools/GeoJson/MultiPolygon.swift
+++ b/Sources/GISTools/GeoJson/MultiPolygon.swift
@@ -26,7 +26,7 @@ public struct MultiPolygon:
 
     public var boundingBox: BoundingBox?
 
-    public var foreignMembers: [String: Any] = [:]
+    public var foreignMembers: [String: Sendable] = [:]
 
     public var polygons: [Polygon] {
         return coordinates.compactMap { Polygon($0) }
diff --git a/Sources/GISTools/GeoJson/Point.swift b/Sources/GISTools/GeoJson/Point.swift
index f59bdd1..fb21fff 100644
--- a/Sources/GISTools/GeoJson/Point.swift
+++ b/Sources/GISTools/GeoJson/Point.swift
@@ -23,7 +23,7 @@ public struct Point: PointGeometry {
 
     public var boundingBox: BoundingBox?
 
-    public var foreignMembers: [String: Any] = [:]
+    public var foreignMembers: [String: Sendable] = [:]
 
     public var points: [Point] {
         return [self]
diff --git a/Sources/GISTools/GeoJson/Polygon.swift b/Sources/GISTools/GeoJson/Polygon.swift
index 5b8d00e..75e644d 100644
--- a/Sources/GISTools/GeoJson/Polygon.swift
+++ b/Sources/GISTools/GeoJson/Polygon.swift
@@ -26,7 +26,7 @@ public struct Polygon:
 
     public var boundingBox: BoundingBox?
 
-    public var foreignMembers: [String: Any] = [:]
+    public var foreignMembers: [String: Sendable] = [:]
 
     public var polygons: [Polygon] {
         return [self]
diff --git a/Sources/GISTools/GeoJson/Projectable.swift b/Sources/GISTools/GeoJson/Projectable.swift
index 859d211..066f1f9 100644
--- a/Sources/GISTools/GeoJson/Projectable.swift
+++ b/Sources/GISTools/GeoJson/Projectable.swift
@@ -9,3 +9,14 @@ public protocol Projectable {
     func projected(to newProjection: Projection) -> Self
 
 }
+
+extension Projectable {
+
+    /// Reproject this coordinate.
+    public mutating func project(to newProjection: Projection) {
+        guard newProjection != projection else { return }
+
+        self = projected(to: newProjection)
+    }
+
+}
diff --git a/Sources/GISTools/GeoJson/RTree.swift b/Sources/GISTools/GeoJson/RTree.swift
index d1109d0..06c9164 100644
--- a/Sources/GISTools/GeoJson/RTree.swift
+++ b/Sources/GISTools/GeoJson/RTree.swift
@@ -33,7 +33,7 @@ public enum RTreeSortOption: Sendable {
 // MARK: - RTree
 
 /// An efficient implementation of the packed Hilbert R-tree algorithm.
-public struct RTree<T: BoundingBoxRepresentable> {
+public struct RTree<T: BoundingBoxRepresentable & Sendable>: Sendable {
 
     /// The R-Tree's `projection`.
     public let projection: Projection
diff --git a/Sources/GISTools/GeoJson/Ring.swift b/Sources/GISTools/GeoJson/Ring.swift
index c62a7e1..00b31c3 100644
--- a/Sources/GISTools/GeoJson/Ring.swift
+++ b/Sources/GISTools/GeoJson/Ring.swift
@@ -14,10 +14,7 @@ import Foundation
 /// - A linear ring MUST follow the right-hand rule with respect to the
 ///   area it bounds, i.e., exterior rings are counterclockwise, and
 ///   holes are clockwise.
-public struct Ring:
-    Projectable,
-    Sendable
-{
+public struct Ring: Sendable {
 
     public var projection: Projection {
         coordinates.first?.projection ?? .noSRID
@@ -47,7 +44,7 @@ public struct Ring:
 
 // MARK: - Projection
 
-extension Ring {
+extension Ring: Projectable {
 
     public func projected(to newProjection: Projection) -> Ring {
         guard newProjection != projection else { return self }
diff --git a/Sources/GISTools/Other/MapTile.swift b/Sources/GISTools/Other/MapTile.swift
index 4c2cec5..f80b8e4 100644
--- a/Sources/GISTools/Other/MapTile.swift
+++ b/Sources/GISTools/Other/MapTile.swift
@@ -3,7 +3,7 @@ import CoreLocation
 #endif
 import Foundation
 
-public struct MapTile: CustomStringConvertible {
+public struct MapTile: CustomStringConvertible, Sendable {
 
     public let x: Int
     public let y: Int
diff --git a/Tests/GISToolsTests/GeoJson/BoundingBoxTests.swift b/Tests/GISToolsTests/GeoJson/BoundingBoxTests.swift
index ce7ea8a..2ffa485 100644
--- a/Tests/GISToolsTests/GeoJson/BoundingBoxTests.swift
+++ b/Tests/GISToolsTests/GeoJson/BoundingBoxTests.swift
@@ -518,4 +518,39 @@ final class BoundingBoxTests: XCTestCase {
         XCTAssertEqual(clamped, BoundingBox.world)
     }
 
+    // MARK: - Expanding
+
+    func testExpanding() throws {
+        let bbox1 = try XCTUnwrap(BoundingBox(coordinates: [.zero]))
+        let bbox1_3857 = bbox1.projected(to: .epsg3857)
+
+        // Note: Expands diagonally
+        let bbox2_3857_distance = bbox1_3857.expanded(byDistance: 1000.0)
+        let bbox2_degrees = bbox1.expanded(byDegrees: 1.0)
+
+        XCTAssertEqual(Coordinate3D.zero.distance(from: bbox2_3857_distance.southWest), 1000.0, accuracy: 0.00001)
+        XCTAssertEqual(Coordinate3D.zero.distance(from: bbox2_3857_distance.northEast), 1000.0, accuracy: 0.00001)
+        XCTAssertEqual(bbox2_degrees.southWest, Coordinate3D(latitude: -1.0, longitude: -1.0))
+        XCTAssertEqual(bbox2_degrees.northEast, Coordinate3D(latitude: 1.0, longitude: 1.0))
+
+        let bbox2_distance = bbox1.expanded(byDistance: 1000.0)
+        let bbox2_3857_degrees = bbox1_3857.expanded(byDegrees: 1.0)
+
+        XCTAssertEqual(bbox2_distance.projected(to: .epsg3857), bbox2_3857_distance)
+        XCTAssertEqual(bbox2_degrees, bbox2_3857_degrees.projected(to: .epsg4326))
+
+        // Note: Expanded horizontally and vertically
+        let bbox3_3857 = try XCTUnwrap(BoundingBox(coordinates: [.zero.projected(to: .epsg3857)], padding: 1000.0))
+        let bbox3_4326 = try XCTUnwrap(BoundingBox(coordinates: [.zero], padding: 1000.0))
+
+        XCTAssertEqual(bbox3_3857.southWest.x, -1000.0, accuracy: 0.00001)
+        XCTAssertEqual(bbox3_3857.southWest.y, -1000.0, accuracy: 0.00001)
+        XCTAssertEqual(bbox3_3857.northEast.x, 1000.0, accuracy: 0.00001)
+        XCTAssertEqual(bbox3_3857.northEast.x, 1000.0, accuracy: 0.00001)
+        XCTAssertEqual(bbox3_4326.projected(to: .epsg3857).southWest.x, bbox3_3857.southWest.x, accuracy: 0.00001)
+        XCTAssertEqual(bbox3_4326.projected(to: .epsg3857).southWest.y, bbox3_3857.southWest.y, accuracy: 0.00001)
+        XCTAssertEqual(bbox3_4326.projected(to: .epsg3857).northEast.x, bbox3_3857.northEast.x, accuracy: 0.00001)
+        XCTAssertEqual(bbox3_4326.projected(to: .epsg3857).northEast.y, bbox3_3857.northEast.y, accuracy: 0.00001)
+    }
+
 }