diff --git a/frontend/src/app/features/schema/helpers/data-mapper.ts b/frontend/src/app/features/schema/helpers/data-mapper.ts
index 2d4061b..3a435c5 100644
--- a/frontend/src/app/features/schema/helpers/data-mapper.ts
+++ b/frontend/src/app/features/schema/helpers/data-mapper.ts
@@ -96,6 +96,7 @@ export function buildGraphData(
         entityType: 'site',
         entityId: site.id,
       },
+      parent: site.parentSiteId ?? undefined,
       zIndex: 1,
     });
   }
diff --git a/frontend/src/app/features/schema/layout/dagre-layout.ts b/frontend/src/app/features/schema/layout/dagre-layout.ts
index 221df38..352c6a3 100644
--- a/frontend/src/app/features/schema/layout/dagre-layout.ts
+++ b/frontend/src/app/features/schema/layout/dagre-layout.ts
@@ -1,149 +1,243 @@
 import dagre from 'dagre';
-import type { Graph, Node } from '@antv/x6';
-import { SITE_PADDING, SITE_HEADER_HEIGHT } from '../../../constants/sizes';
+import type { Graph, Node, Cell } from '@antv/x6';
+import { LAYER_MAPPING } from '../../../constants/layer-mapping';
+import {
+  SITE_PADDING,
+  SITE_HEADER_HEIGHT,
+} from '../../../constants/sizes';
+
+function getLayerForCategory(category: string): number {
+  for (const [layer, categories] of Object.entries(LAYER_MAPPING)) {
+    if ((categories as string[]).includes(category)) {
+      return parseInt(layer, 10);
+    }
+  }
+  return 7;
+}
 
-/**
- * Resolves a cell ID to its top-level device node ID.
- * If the cell is a card, returns the parent device ID.
- * If the cell is a device, returns its own ID.
- * Returns null for site nodes or unknown cells.
- */
 function resolveDeviceId(graph: Graph, cellId: string): string | null {
   const cell = graph.getCellById(cellId);
   if (!cell || !cell.isNode()) return null;
-  const shape = cell.shape;
-  if (shape === 'site-node') return null;
-  if (shape === 'card-node') {
-    const parent = cell.getParent();
+  if (cell.shape === 'site-node') return null;
+  if (cell.shape === 'card-node') {
+    const parent = (cell as Node).getParent();
     return parent ? parent.id : null;
   }
   return cell.id;
 }
 
+interface DeviceEdge {
+  source: string;
+  target: string;
+}
+
 /**
- * Applies dagre hierarchical layout to the graph.
- * Devices are positioned by dagre based on their connections.
- * Site containers are then recalculated to wrap their children.
+ * Layout devices within a single site using dagre.
+ * Uses LAYER_MAPPING to enforce vertical hierarchy via invisible edges.
+ * Returns the bounding box size of the laid-out devices.
  */
-export function applyDagreLayout(graph: Graph): void {
-  const allNodes = graph.getNodes();
-  const allEdges = graph.getEdges();
+function layoutSiteDevices(
+  graph: Graph,
+  devices: Node[],
+  edges: DeviceEdge[],
+  offsetX: number,
+  offsetY: number,
+): { width: number; height: number } {
+  if (devices.length === 0) return { width: 250, height: 150 };
 
-  const siteNodes = allNodes.filter((n) => n.shape === 'site-node');
-  const deviceNodes = allNodes.filter(
-    (n) => n.shape !== 'site-node' && n.shape !== 'card-node',
-  );
-
-  if (deviceNodes.length === 0) return;
-
-  // Build dagre graph
   const g = new dagre.graphlib.Graph();
   g.setDefaultEdgeLabel(() => ({}));
   g.setGraph({
     rankdir: 'TB',
     nodesep: 50,
     ranksep: 70,
-    marginx: 50,
-    marginy: 50,
+    marginx: 20,
+    marginy: 20,
   });
 
-  for (const node of deviceNodes) {
-    const size = node.getSize();
-    g.setNode(node.id, { width: size.width, height: size.height });
+  const deviceIdSet = new Set(devices.map((d) => d.id));
+
+  // Group by layer
+  const layerGroups = new Map<number, Node[]>();
+  for (const device of devices) {
+    const data = device.getData<{ category?: string }>();
+    const layer = getLayerForCategory(data?.category ?? '');
+    const group = layerGroups.get(layer) ?? [];
+    group.push(device);
+    layerGroups.set(layer, group);
   }
 
-  // Deduplicate edges at device level
+  // Add nodes
+  for (const device of devices) {
+    const size = device.getSize();
+    g.setNode(device.id, { width: size.width, height: size.height });
+  }
+
+  // Add real edges within this site (deduplicated)
   const edgeSet = new Set<string>();
-  for (const edge of allEdges) {
-    const sourceDevice = resolveDeviceId(graph, edge.getSourceCellId());
-    const targetDevice = resolveDeviceId(graph, edge.getTargetCellId());
-    if (!sourceDevice || !targetDevice) continue;
-    if (sourceDevice === targetDevice) continue; // skip self-loops
-    const key = `${sourceDevice}->${targetDevice}`;
+  for (const { source, target } of edges) {
+    if (!deviceIdSet.has(source) || !deviceIdSet.has(target)) continue;
+    if (source === target) continue;
+    const key = `${source}->${target}`;
     if (edgeSet.has(key)) continue;
     edgeSet.add(key);
-    g.setEdge(sourceDevice, targetDevice);
+    g.setEdge(source, target);
+  }
+
+  // Add invisible edges between consecutive layers to enforce hierarchy
+  const sortedLayers = [...layerGroups.keys()].sort((a, b) => a - b);
+  for (let i = 0; i < sortedLayers.length - 1; i++) {
+    const upper = layerGroups.get(sortedLayers[i])!;
+    const lower = layerGroups.get(sortedLayers[i + 1])!;
+    const key = `${upper[0].id}->${lower[0].id}`;
+    if (!edgeSet.has(key)) {
+      edgeSet.add(key);
+      g.setEdge(upper[0].id, lower[0].id, { weight: 0, minlen: 1 });
+    }
   }
 
   dagre.layout(g);
 
-  // Apply positions inside a batch for single undo step
-  graph.startBatch('dagre-layout');
-
+  // Apply positions with offset (dagre returns center coords)
   for (const nodeId of g.nodes()) {
+    if (nodeId.startsWith('_dummy_')) continue;
     const pos = g.node(nodeId);
     const node = graph.getCellById(nodeId) as Node | undefined;
     if (node && pos) {
-      // dagre returns center coordinates, convert to top-left
-      node.setPosition(pos.x - pos.width / 2, pos.y - pos.height / 2);
+      node.setPosition(
+        offsetX + pos.x - pos.width / 2,
+        offsetY + pos.y - pos.height / 2,
+      );
     }
   }
 
-  // Recalculate site containers to wrap their device children
-  // Process child sites first (those whose devices are inside another site)
-  // We detect hierarchy by checking which sites share devices
-  const siteById = new Map<string, Node>();
-  for (const site of siteNodes) {
-    siteById.set(site.id, site);
+  const graphInfo = g.graph();
+  return {
+    width: graphInfo.width ?? 250,
+    height: graphInfo.height ?? 150,
+  };
+}
+
+/**
+ * Applies dagre hierarchical layout to the entire graph.
+ * - Each site is laid out independently (per-site dagre)
+ * - LAYER_MAPPING enforces vertical device hierarchy
+ * - Sites are positioned in a row
+ * - Site containers are recalculated to wrap their children
+ */
+export function applyDagreLayout(graph: Graph): void {
+  const allNodes = graph.getNodes();
+  const allEdges = graph.getEdges();
+
+  const siteNodes = allNodes.filter((n) => n.shape === 'site-node');
+  if (siteNodes.length === 0) return;
+
+  // Pre-compute all device-level edges
+  const deviceEdges: DeviceEdge[] = [];
+  const edgeDedup = new Set<string>();
+  for (const edge of allEdges) {
+    const source = resolveDeviceId(graph, edge.getSourceCellId());
+    const target = resolveDeviceId(graph, edge.getTargetCellId());
+    if (!source || !target || source === target) continue;
+    const key = `${source}->${target}`;
+    if (edgeDedup.has(key)) continue;
+    edgeDedup.add(key);
+    deviceEdges.push({ source, target });
   }
 
-  // Build site → direct children (devices) map via X6 embedding
-  const siteChildren = new Map<string, Node[]>();
-  for (const site of siteNodes) {
-    const children = (site.getChildren() ?? []).filter(
-      (c): c is Node => c.isNode() && c.shape !== 'site-node',
-    );
-    siteChildren.set(site.id, children);
-  }
-
-  // Detect child sites: a site whose bounding box center is inside another site
-  // We use the data approach: check if any site is a child of another
-  // Sort: leaf sites first (those with no child sites inside them)
+  // Detect child sites (embedded in parent site via X6)
   const childSiteIds = new Set<string>();
   for (const site of siteNodes) {
-    const children = (site.getChildren() ?? []).filter(
-      (c): c is Node => c.isNode() && c.shape === 'site-node',
-    );
+    const children = site.getChildren() ?? [];
     for (const child of children) {
-      childSiteIds.add(child.id);
+      if (child.isNode() && child.shape === 'site-node') {
+        childSiteIds.add(child.id);
+      }
     }
   }
 
-  // First pass: resize child sites (leaf sites)
-  const sortedSites = [
-    ...siteNodes.filter((s) => childSiteIds.has(s.id)),
-    ...siteNodes.filter((s) => !childSiteIds.has(s.id)),
-  ];
+  const rootSites = siteNodes.filter((s) => !childSiteIds.has(s.id));
 
-  for (const site of sortedSites) {
-    const children = site.getChildren() ?? [];
-    const childNodes = children.filter((c): c is Node => c.isNode());
-    if (childNodes.length === 0) continue;
+  graph.startBatch('dagre-layout');
 
-    let minX = Infinity;
-    let minY = Infinity;
-    let maxX = -Infinity;
-    let maxY = -Infinity;
+  let cursorX = 50;
+  const siteGap = 120;
+  const startY = 50;
 
-    for (const child of childNodes) {
-      const pos = child.getPosition();
-      const size = child.getSize();
-      minX = Math.min(minX, pos.x);
-      minY = Math.min(minY, pos.y);
-      maxX = Math.max(maxX, pos.x + size.width);
-      maxY = Math.max(maxY, pos.y + size.height);
+  for (const rootSite of rootSites) {
+    // Get direct device children of this root site
+    const rootDevices = getDeviceChildren(rootSite);
+
+    // Layout root site's own devices
+    const devicesStartY = startY + SITE_HEADER_HEIGHT + SITE_PADDING;
+    const rootResult = layoutSiteDevices(
+      graph,
+      rootDevices,
+      deviceEdges,
+      cursorX + SITE_PADDING,
+      devicesStartY,
+    );
+
+    // Find child sites of this root site
+    const childSites = (rootSite.getChildren() ?? []).filter(
+      (c): c is Node => c.isNode() && c.shape === 'site-node',
+    );
+
+    let childCursorX = cursorX + SITE_PADDING;
+    let childSitesMaxHeight = 0;
+    const childSiteYStart = devicesStartY + rootResult.height + SITE_PADDING;
+
+    for (const childSite of childSites) {
+      const childDevices = getDeviceChildren(childSite);
+      const childDevicesY = childSiteYStart + SITE_HEADER_HEIGHT + SITE_PADDING;
+
+      const childResult = layoutSiteDevices(
+        graph,
+        childDevices,
+        deviceEdges,
+        childCursorX + SITE_PADDING,
+        childDevicesY,
+      );
+
+      const childWidth = Math.max(childResult.width + SITE_PADDING * 2, 250);
+      const childHeight = childResult.height + SITE_HEADER_HEIGHT + SITE_PADDING * 2;
+
+      childSite.setPosition(childCursorX, childSiteYStart);
+      childSite.setSize(childWidth, childHeight);
+
+      childCursorX += childWidth + 40;
+      childSitesMaxHeight = Math.max(childSitesMaxHeight, childHeight);
     }
 
-    if (!isFinite(minX)) continue;
+    const childSitesTotalWidth = childCursorX - (cursorX + SITE_PADDING);
+    const childSitesExtra =
+      childSites.length > 0 ? childSitesMaxHeight + SITE_PADDING : 0;
 
-    const newX = minX - SITE_PADDING;
-    const newY = minY - SITE_HEADER_HEIGHT - SITE_PADDING;
-    const newWidth = maxX - minX + SITE_PADDING * 2;
-    const newHeight = maxY - minY + SITE_HEADER_HEIGHT + SITE_PADDING * 2;
+    // Calculate root site bounds
+    const rootWidth = Math.max(
+      rootResult.width + SITE_PADDING * 2,
+      childSitesTotalWidth,
+      250,
+    );
+    const rootHeight =
+      SITE_HEADER_HEIGHT +
+      SITE_PADDING +
+      rootResult.height +
+      childSitesExtra +
+      SITE_PADDING;
 
-    site.setPosition(newX, newY);
-    site.setSize(Math.max(newWidth, 250), Math.max(newHeight, 150));
+    rootSite.setPosition(cursorX, startY);
+    rootSite.setSize(rootWidth, rootHeight);
+
+    cursorX += rootWidth + siteGap;
   }
 
   graph.stopBatch('dagre-layout');
 }
+
+function getDeviceChildren(siteNode: Node): Node[] {
+  return (siteNode.getChildren() ?? []).filter(
+    (c): c is Node =>
+      c.isNode() && c.shape !== 'site-node' && c.shape !== 'card-node',
+  );
+}