diff --git a/src/core/region.ts b/src/core/region.ts
index ea9f907..5ecd0e0 100644
--- a/src/core/region.ts
+++ b/src/core/region.ts
@@ -1,3 +1,4 @@
+import {computed, ReadonlySignal, SignalOptions} from "@preact/signals-core";
 import {Entity} from "@/utils/entity";
 import {Part} from "./part";
 import {RNG} from "@/utils/rng";
@@ -15,6 +16,22 @@ export type RegionAxis = {
   align?: 'start' | 'end' | 'center';
 }
 
+export class RegionEntity extends Entity<Region> {
+  public readonly partsMap: ReadonlySignal<Record<string, Entity<Part>>>;
+
+  public constructor(id: string, t?: Region, options?: SignalOptions<Region>) {
+    super(id, t, options);
+    this.partsMap = computed(() => {
+      const result: Record<string, Entity<Part>> = {};
+      for (const child of this.value.children) {
+        const key = child.value.position.join(',');
+        result[key] = child;
+      }
+      return result;
+    });
+  }
+}
+
 export function applyAlign(region: Entity<Region>) {
   region.produce(applyAlignCore);
 }