diff --git a/src/mapper/mapper.cc b/src/mapper/mapper.cc
new file mode 100644
index 0000000..a3885e9
--- /dev/null
+++ b/src/mapper/mapper.cc
@@ -0,0 +1,30 @@
+#include "mapper/mapper.h"
+
+#include "object.h"
+#include "proto.h"
+
+namespace fallout {
+
+static void mapper_mark_all_exit_grids();
+
+// 0x559748
+MapTransition mapInfo = { -1, -1, 0, 0 };
+
+// 0x48C704
+void mapper_mark_all_exit_grids()
+{
+    Object* obj;
+
+    obj = objectFindFirstAtElevation(gElevation);
+    while (obj != NULL) {
+        if (isExitGridPid(obj->pid)) {
+            obj->data.misc.map = mapInfo.map;
+            obj->data.misc.tile = mapInfo.tile;
+            obj->data.misc.elevation = mapInfo.elevation;
+            obj->data.misc.rotation = mapInfo.rotation;
+        }
+        obj = objectFindNextAtElevation();
+    }
+}
+
+} // namespace fallout
diff --git a/src/mapper/mapper.h b/src/mapper/mapper.h
new file mode 100644
index 0000000..3d6adb3
--- /dev/null
+++ b/src/mapper/mapper.h
@@ -0,0 +1,12 @@
+#ifndef FALLOUT_MAPPER_MAPPER_H_
+#define FALLOUT_MAPPER_MAPPER_H_
+
+#include "map.h"
+
+namespace fallout {
+
+extern MapTransition mapInfo;
+
+} // namespace fallout
+
+#endif /* FALLOUT_MAPPER_MAPPER_H_ */