diff --git a/app/ecs/schema.js b/app/ecs/schema.js
index dafb4fb..a379f65 100644
--- a/app/ecs/schema.js
+++ b/app/ecs/schema.js
@@ -53,6 +53,16 @@ export default class Schema {
         }
         return value;
       }
+      case 'map': {
+        const length = view.getUint32(offset.value, true);
+        offset.value += 4;
+        const value = {};
+        for (let i = 0; i < length; ++i) {
+          const key = this.deserialize(view, offset, {type: 'string'});
+          value[key] = this.deserialize(view, offset, specification.value);
+        }
+        return value;
+      }
       case 'object': {
         const value = {};
         for (const key in specification.properties) {
@@ -92,6 +102,9 @@ export default class Schema {
       case 'array': {
         return [];
       }
+      case 'map': {
+        return {};
+      }
       case 'object': {
         const object = {};
         for (const key in specification.properties) {
@@ -109,10 +122,6 @@ export default class Schema {
     return this.constructor.defaultValue(this.specification);
   }
 
-  has(key) {
-    return key in this.specification;
-  }
-
   static normalize(specification) {
     let normalized = specification;
     switch (specification.type) {
@@ -120,6 +129,10 @@ export default class Schema {
         normalized.subtype = this.normalize(specification.subtype);
         break;
       }
+      case 'map': {
+        normalized.value = this.normalize(specification.value);
+        break;
+      }
       case 'object': {
         for (const key in specification.properties) {
           normalized.properties[key] = this.normalize(specification.properties[key])
@@ -139,6 +152,7 @@ export default class Schema {
       case 'string': {
         break;
       }
+      /* v8 ignore next 2 */
       default:
         throw new TypeError(`invalid specification: ${JSON.stringify(specification)}`);
     }
@@ -154,8 +168,7 @@ export default class Schema {
     switch (specification.type) {
       case 'array': {
         view.setUint32(offset, source.length, true);
-        offset += 4;
-        let arraySize = 0;
+        let arraySize = 4;
         for (const element of source) {
           arraySize += this.serialize(
             element,
@@ -164,7 +177,27 @@ export default class Schema {
             specification.subtype,
           );
         }
-        return 4 + arraySize;
+        return arraySize;
+      }
+      case 'map': {
+        const keys = Object.keys(source);
+        view.setUint32(offset, keys.length, true);
+        let mapSize = 4;
+        for (const key of keys) {
+          mapSize += this.serialize(
+            key,
+            view,
+            offset + mapSize,
+            {type: 'string'},
+          );
+          mapSize += this.serialize(
+            source[key],
+            view,
+            offset + mapSize,
+            specification.value,
+          );
+        }
+        return mapSize;
       }
       case 'object': {
         let objectSize = 0;
@@ -210,6 +243,14 @@ export default class Schema {
         }
         break;
       }
+      case 'map': {
+        fullSize += 4;
+        for (const key in concrete) {
+          fullSize += this.sizeOf(key, {type: 'string'});
+          fullSize += this.sizeOf(concrete[key], specification.value);
+        }
+        break;
+      }
       case 'object': {
         for (const key in specification.properties) {
           fullSize += this.sizeOf(concrete[key], specification.properties[key]);
@@ -231,6 +272,7 @@ export default class Schema {
   static size(specification) {
     switch (specification.type) {
       case 'array': return 0;
+      case 'map': return 0; // TODO could be fixed-size w/ fixed-size key
       case 'object': {
         let size = 0;
         for (const key in specification.properties) {
@@ -258,8 +300,4 @@ export default class Schema {
     }
   }
 
-  size() {
-    return this.constructor.size(this.specification);
-  }
-
 }
diff --git a/app/ecs/schema.test.js b/app/ecs/schema.test.js
index 3ee5eb4..50a1d5d 100644
--- a/app/ecs/schema.test.js
+++ b/app/ecs/schema.test.js
@@ -3,6 +3,14 @@ import {expect, test} from 'vitest';
 import Schema from './schema.js';
 
 test('defaults values', () => {
+  const compare = (specification, value) => {
+    expect(Schema.defaultValue(specification))
+      .to.deep.equal(value);
+    expect(new Schema(specification).specification.defaultValue)
+      .to.deep.equal(value);
+    expect(new Schema(specification).defaultValue())
+      .to.deep.equal(value);
+  };
   [
     'uint8',
     'int8',
@@ -15,37 +23,35 @@ test('defaults values', () => {
     'float32',
     'float64',
   ].forEach((type) => {
-    expect(Schema.defaultValue({type}))
-      .to.equal(0);
-    expect(new Schema({type}).specification.defaultValue)
-      .to.equal(0);
+    compare({type}, 0);
   });
-  expect(Schema.defaultValue({type: 'string'}))
-    .to.equal('');
-  expect(new Schema({type: 'string'}).specification.defaultValue)
-    .to.equal('');
-  expect(Schema.defaultValue({type: 'array', subtype: {type: 'string'}}))
-    .to.deep.equal([]);
-  expect(new Schema({type: 'array', subtype: {type: 'string'}}).specification.defaultValue)
-    .to.deep.equal([]);
-  expect(Schema.defaultValue({
-    type: 'object',
-    properties: {
-      foo: {type: 'uint8'},
-      bar: {type: 'string'},
-      baz: {type: 'object', properties: {blah: {type: 'array', subtype: {type: 'string'}}}},
+  compare({type: 'string'}, '');
+  compare({type: 'array', subtype: {type: 'string'}}, []);
+  compare(
+    {
+      type: 'object',
+      properties: {
+        foo: {type: 'uint8'},
+        bar: {type: 'string'},
+        baz: {type: 'object', properties: {blah: {type: 'array', subtype: {type: 'string'}}}},
+      },
     },
-  }))
-    .to.deep.equal({foo: 0, bar: '', baz: {blah: []}});
-  expect(new Schema({
-    type: 'object',
-    properties: {
-      foo: {type: 'uint8'},
-      bar: {type: 'string'},
-      baz: {type: 'object', properties: {blah: {type: 'array', subtype: {type: 'string'}}}},
+    {foo: 0, bar: '', baz: {blah: []}},
+  );
+  compare(
+    {
+      type: 'map',
+      value: {
+        type: 'object',
+        properties: {
+          foo: {type: 'uint8'},
+          bar: {type: 'string'},
+          baz: {type: 'object', properties: {blah: {type: 'array', subtype: {type: 'string'}}}},
+        },
+      },
     },
-  }).specification.defaultValue)
-    .to.deep.equal({foo: 0, bar: '', baz: {blah: []}});
+    {},
+  );
 });
 
 test('validates a schema', () => {
@@ -66,6 +72,7 @@ test('validates a schema', () => {
       new Schema({type});
       new Schema({type: 'array', subtype: {type}});
       new Schema({type: 'object', properties: {foo: {type}}});
+      new Schema({type: 'map', value: {type}});
     })
       .to.not.throw();
   });
@@ -77,14 +84,16 @@ test('calculates the size of concrete instances', () => {
       .sizeOf('hi')
   )
     .to.equal(4 + (new TextEncoder().encode('hi')).length);
-
   expect(
     (new Schema(
-      {type: 'object', properties: {
-        foo: {type: 'uint8'},
-        bar: {type: 'uint32'},
-        baz: {type: 'string'},
-      }}
+      {
+        type: 'object',
+        properties: {
+          foo: {type: 'uint8'},
+          bar: {type: 'uint32'},
+          baz: {type: 'string'},
+        },
+      },
     ))
       .sizeOf({foo: 69, bar: 420, baz: 'aα'})
   )
@@ -102,6 +111,36 @@ test('calculates the size of concrete instances', () => {
       + 4 + (new TextEncoder().encode('hallo')).length
       + 4 + (new TextEncoder().encode('hαllo')).length
     );
+  expect(
+    (new Schema(
+      {
+        type: 'map',
+        value: {
+          type: 'object',
+          properties: {
+            foo: {type: 'uint8'},
+            bar: {type: 'uint32'},
+            baz: {type: 'string'},
+          },
+        },
+      },
+    ))
+      .sizeOf({
+        foo: {foo: 69, bar: 420, baz: 'aα'},
+        'aα': {foo: 69, bar: 420, baz: 'meow'},
+      })
+  )
+    .to.equal(
+      4
+      + 4 + (new TextEncoder().encode('foo')).length
+      + 1
+      + 4
+      + 4 + (new TextEncoder().encode('aα')).length
+      + 4 + (new TextEncoder().encode('aα')).length
+      + 1
+      + 4
+      + 4 + (new TextEncoder().encode('meow')).length
+    );
 });
 
 test('encodes and decodes', () => {
@@ -124,7 +163,9 @@ test('encodes and decodes', () => {
     [{type: 'string'}, 'α'],
     [{type: 'array', subtype: {type: 'uint8'}}, [1, 2, 3, 4]],
     [{type: 'array', subtype: {type: 'string'}}, ['one', 'two', 'three', 'four']],
+    [{type: 'map', value: {type: 'object', properties: {foo: {type: 'uint8'}, bar: {type: 'string'}}}}, {one: {foo: 64, bar: 'baz'}, two: {foo: 128, bar: 'baw'}}],
     [{type: 'object', properties: {foo: {type: 'uint8'}, bar: {type: 'string'}}}, {foo: 64, bar: 'baz'}],
+    [{type: 'object', properties: {foo: {type: 'uint8'}}}, {foo: 64}],
   ];
   entries.forEach(([specification, concrete]) => {
     const schema = new Schema(specification);