diff --git a/Sources/MapConductorForGoogleMaps/circle/GoogleMapCircleOverlayRenderer.swift b/Sources/MapConductorForGoogleMaps/circle/GoogleMapCircleOverlayRenderer.swift
index ba8a58f..9c90c48 100644
--- a/Sources/MapConductorForGoogleMaps/circle/GoogleMapCircleOverlayRenderer.swift
+++ b/Sources/MapConductorForGoogleMaps/circle/GoogleMapCircleOverlayRenderer.swift
@@ -1,6 +1,6 @@
 import CoreLocation
 import GoogleMaps
-import MapConductorCore
+@_spi(MapConductorDriver) import MapConductorCore
 import UIKit
 
 @MainActor
@@ -25,7 +25,7 @@ final class GoogleMapCircleOverlayRenderer: AbstractCircleOverlayRenderer<GMSPol
         // Use mapView(_:didTapAt:) + CircleManager hit-testing for click handling.
         // If we set this tappable, Google Maps consumes taps and we'd need mapView(_:didTap:) overlay handling.
         polygon.isTappable = false
-        polygon.zIndex = Int32(state.zIndex ?? 0)
+        polygon.zIndex = OverlayStacking.globalZIndex(OverlayStackKey(.circle, zIndex: state.zIndex ?? 0))
         polygon.geodesic = state.geodesic
         polygon.map = mapView
         polygon.userData = state.id
@@ -71,7 +71,7 @@ final class GoogleMapCircleOverlayRenderer: AbstractCircleOverlayRenderer<GMSPol
         }
 
         if finger.zIndex != prevFinger.zIndex {
-            circle.zIndex = Int32(current.state.zIndex ?? 0)
+            circle.zIndex = OverlayStacking.globalZIndex(OverlayStackKey(.circle, zIndex: current.state.zIndex ?? 0))
         }
 
         return circle
diff --git a/Sources/MapConductorForGoogleMaps/groundimage/GoogleMapGroundImageOverlayRenderer.swift b/Sources/MapConductorForGoogleMaps/groundimage/GoogleMapGroundImageOverlayRenderer.swift
index d3401b3..738fbeb 100644
--- a/Sources/MapConductorForGoogleMaps/groundimage/GoogleMapGroundImageOverlayRenderer.swift
+++ b/Sources/MapConductorForGoogleMaps/groundimage/GoogleMapGroundImageOverlayRenderer.swift
@@ -1,6 +1,6 @@
 import CoreLocation
 import GoogleMaps
-import MapConductorCore
+@_spi(MapConductorDriver) import MapConductorCore
 
 @MainActor
 final class GoogleMapGroundImageOverlayRenderer: AbstractGroundImageOverlayRenderer<GMSGroundOverlay> {
@@ -16,6 +16,7 @@ final class GoogleMapGroundImageOverlayRenderer: AbstractGroundImageOverlayRende
         guard let bounds = toCoordinateBounds(state.bounds) else { return nil }
 
         let overlay = GMSGroundOverlay(bounds: bounds, icon: state.image)
+        overlay.zIndex = OverlayStacking.globalZIndex(OverlayStackKey(.groundImage, zIndex: 0))
         overlay.opacity = Float(state.opacity)
         overlay.isTappable = false
         overlay.userData = state.id
diff --git a/Sources/MapConductorForGoogleMaps/marker/GoogleMapMarkerController.swift b/Sources/MapConductorForGoogleMaps/marker/GoogleMapMarkerController.swift
index 85738e5..c75b776 100644
--- a/Sources/MapConductorForGoogleMaps/marker/GoogleMapMarkerController.swift
+++ b/Sources/MapConductorForGoogleMaps/marker/GoogleMapMarkerController.swift
@@ -359,7 +359,8 @@ final class GoogleMapMarkerController: AbstractMarkerController<GMSMarker, Googl
         // タイル差し替え時のフェードを切る。フェード中の升は古い絵と新しい絵の
         // 合成で、そこにジェスチャが重なると途中の絵が残ることがある。
         layer.fadeIn = false
-        layer.zIndex = 0
+        // マーカーのタイルはマーカーと同じ帯（GMSTileLayer の zIndex はポリゴン等と比べられる）。
+        layer.zIndex = OverlayStacking.globalZIndex(OverlayStackKey(.marker, zIndex: 0))
         layer.map = mapView
         tileTileLayer = layer
     }
diff --git a/Sources/MapConductorForGoogleMaps/marker/GoogleMapMarkerRenderer.swift b/Sources/MapConductorForGoogleMaps/marker/GoogleMapMarkerRenderer.swift
index ba075dc..471dd1d 100644
--- a/Sources/MapConductorForGoogleMaps/marker/GoogleMapMarkerRenderer.swift
+++ b/Sources/MapConductorForGoogleMaps/marker/GoogleMapMarkerRenderer.swift
@@ -1,7 +1,7 @@
 import CoreGraphics
 import CoreLocation
 import GoogleMaps
-import MapConductorCore
+@_spi(MapConductorDriver) import MapConductorCore
 
 @MainActor
 final class GoogleMapMarkerRenderer: MarkerOverlayRendererProtocol {
@@ -295,7 +295,7 @@ final class GoogleMapMarkerRenderer: MarkerOverlayRendererProtocol {
         marker.isTappable = state.clickable
         marker.icon = bitmapIcon.bitmap
         marker.groundAnchor = bitmapIcon.anchor
-        marker.zIndex = Int32(state.zIndex ?? 0)
+        marker.zIndex = OverlayStacking.globalZIndex(OverlayStackKey(.marker, zIndex: state.zIndex ?? 0))
         // Avoid a 1-frame "flash" at the target position when an animation is specified at
         // construction (or during a state update). Keep it hidden until `onAnimate` repositions
         // it to the offscreen start point.
diff --git a/Sources/MapConductorForGoogleMaps/polygon/GoogleMapPolygonOverlayRenderer.swift b/Sources/MapConductorForGoogleMaps/polygon/GoogleMapPolygonOverlayRenderer.swift
index b9c57cc..d6715cd 100644
--- a/Sources/MapConductorForGoogleMaps/polygon/GoogleMapPolygonOverlayRenderer.swift
+++ b/Sources/MapConductorForGoogleMaps/polygon/GoogleMapPolygonOverlayRenderer.swift
@@ -1,5 +1,5 @@
 import GoogleMaps
-import MapConductorCore
+@_spi(MapConductorDriver) import MapConductorCore
 import UIKit
 
 @MainActor
@@ -22,7 +22,7 @@ final class GoogleMapPolygonOverlayRenderer: AbstractPolygonOverlayRenderer<GMSP
         polygon.strokeWidth = CGFloat(resolved.strokeWidth)
         polygon.fillColor = resolved.fillColor
         polygon.geodesic = resolved.geodesic
-        polygon.zIndex = Int32(truncatingIfNeeded: resolved.zIndex)
+        polygon.zIndex = OverlayStacking.globalZIndex(OverlayStackKey(.polygon, zIndex: resolved.zIndex))
         polygon.holes = resolved.holes.map { holePoints in
             ringPath(for: holePoints, geodesic: resolved.geodesic, mapView: mapView)
         }
@@ -62,7 +62,7 @@ final class GoogleMapPolygonOverlayRenderer: AbstractPolygonOverlayRenderer<GMSP
         }
 
         if finger.zIndex != prevFinger.zIndex {
-            polygon.zIndex = Int32(truncatingIfNeeded: current.state.zIndex)
+            polygon.zIndex = OverlayStacking.globalZIndex(OverlayStackKey(.polygon, zIndex: current.state.zIndex))
         }
 
         return polygon
diff --git a/Sources/MapConductorForGoogleMaps/polyline/GoogleMapPolylineOverlayRenderer.swift b/Sources/MapConductorForGoogleMaps/polyline/GoogleMapPolylineOverlayRenderer.swift
index e2e1b63..b5cff0e 100644
--- a/Sources/MapConductorForGoogleMaps/polyline/GoogleMapPolylineOverlayRenderer.swift
+++ b/Sources/MapConductorForGoogleMaps/polyline/GoogleMapPolylineOverlayRenderer.swift
@@ -1,5 +1,5 @@
 import GoogleMaps
-import MapConductorCore
+@_spi(MapConductorDriver) import MapConductorCore
 import UIKit
 
 @MainActor
@@ -21,7 +21,7 @@ final class GoogleMapPolylineOverlayRenderer: AbstractPolylineOverlayRenderer<GM
         polyline.strokeWidth = CGFloat(state.strokeWidth)
         polyline.geodesic = state.geodesic
         polyline.isTappable = false
-        polyline.zIndex = Int32(state.zIndex)
+        polyline.zIndex = OverlayStacking.globalZIndex(OverlayStackKey(.polyline, zIndex: state.zIndex))
         polyline.map = mapView
         polyline.userData = state.id
         return polyline
@@ -50,7 +50,7 @@ final class GoogleMapPolylineOverlayRenderer: AbstractPolylineOverlayRenderer<GM
         }
 
         if finger.zIndex != prevFinger.zIndex {
-            polyline.zIndex = Int32(current.state.zIndex)
+            polyline.zIndex = OverlayStacking.globalZIndex(OverlayStackKey(.polyline, zIndex: current.state.zIndex))
         }
 
         return polyline
diff --git a/Sources/MapConductorForGoogleMaps/raster/GoogleMapRasterLayerOverlayRenderer.swift b/Sources/MapConductorForGoogleMaps/raster/GoogleMapRasterLayerOverlayRenderer.swift
index a260f4d..c95d4be 100644
--- a/Sources/MapConductorForGoogleMaps/raster/GoogleMapRasterLayerOverlayRenderer.swift
+++ b/Sources/MapConductorForGoogleMaps/raster/GoogleMapRasterLayerOverlayRenderer.swift
@@ -1,5 +1,5 @@
 import GoogleMaps
-import MapConductorCore
+@_spi(MapConductorDriver) import MapConductorCore
 import UIKit
 
 @MainActor
@@ -18,7 +18,7 @@ final class GoogleMapRasterLayerOverlayRenderer: AbstractRasterLayerOverlayRende
         guard let mapView else { return nil }
         guard let layer = makeTileLayer(from: state) else { return nil }
         layer.opacity = Float(state.opacity)
-        layer.zIndex = Int32(clamping: state.zIndex)
+        layer.zIndex = OverlayStacking.globalZIndex(OverlayStacking.rasterKey(stateId: state.id, zIndex: state.zIndex))
         applyVisibility(layer: layer, state: state, mapView: mapView)
         return layer
     }
@@ -48,7 +48,7 @@ final class GoogleMapRasterLayerOverlayRenderer: AbstractRasterLayerOverlayRende
             guard let mapView else { return nil }
             guard let newLayer = makeTileLayer(from: current.state) else { return nil }
             newLayer.opacity = Float(current.state.opacity)
-            newLayer.zIndex = Int32(clamping: current.state.zIndex)
+            newLayer.zIndex = OverlayStacking.globalZIndex(OverlayStacking.rasterKey(stateId: current.state.id, zIndex: current.state.zIndex))
             applyVisibility(layer: newLayer, state: current.state, mapView: mapView)
             return newLayer
         }
@@ -58,7 +58,7 @@ final class GoogleMapRasterLayerOverlayRenderer: AbstractRasterLayerOverlayRende
         }
 
         if finger.zIndex != prevFinger.zIndex {
-            layer.zIndex = Int32(clamping: current.state.zIndex)
+            layer.zIndex = OverlayStacking.globalZIndex(OverlayStacking.rasterKey(stateId: current.state.id, zIndex: current.state.zIndex))
         }
 
         if finger.visible != prevFinger.visible {
@@ -84,7 +84,7 @@ final class GoogleMapRasterLayerOverlayRenderer: AbstractRasterLayerOverlayRende
             tileSources.removeValue(forKey: ObjectIdentifier(local))
             localLayers.removeValue(forKey: ObjectIdentifier(local))
             next.opacity = Float(current.state.opacity)
-            next.zIndex = Int32(clamping: current.state.zIndex)
+            next.zIndex = OverlayStacking.globalZIndex(OverlayStacking.rasterKey(stateId: current.state.id, zIndex: current.state.zIndex))
             applyVisibility(layer: next, state: current.state, mapView: mapView)
             return next
         }