Index: trunk/data/maps.xsd
===================================================================
--- trunk/data/maps.xsd	(revision 14541)
+++ trunk/data/maps.xsd	(revision 14552)
@@ -643,5 +643,5 @@
                             <xs:element name="description" minOccurs="0" type="tns:description" />
                             <!-- A unique id for the imagery source -->
-                            <xs:element name="id" minOccurs="0" maxOccurs="1" type="tns:id" />
+                            <xs:element name="id" minOccurs="1" maxOccurs="1" type="tns:id" />
                             <!-- Historic id for the imagery source -->
                             <xs:element name="oldid" minOccurs="0" maxOccurs="unbounded" type="tns:oldid" />