diff --git a/lib/waterfoul/map.rb b/lib/waterfoul/map.rb
new file mode 100644
index 0000000..ac66edc
--- /dev/null
+++ b/lib/waterfoul/map.rb
@@ -0,0 +1,17 @@
+module Waterfoul
+  class Map
+    MAP_0_START_ADDR = 0x0
+    MAP_1_START_ADDR = 0x0
+
+    def initialize(map_no = 0)
+      map_number map_no
+    end
+
+    def map_number(map_no)
+      raise 'unknown map number' unless [0, 1].include? map_no
+    end
+
+    def tiles
+    end
+  end
+end