Index: trunk/data/maps.xsd
===================================================================
--- trunk/data/maps.xsd	(revision 7176)
+++ trunk/data/maps.xsd	(revision 7177)
@@ -14,4 +14,11 @@
 			<xs:minInclusive value="-180" />
 			<xs:maxInclusive value="+180" />
+		</xs:restriction>
+	</xs:simpleType>
+	
+	<xs:simpleType name="id">
+        <!-- exclude white space characters and characters that are not valid for file names in Windows -->
+		<xs:restriction base="xs:string">
+			<xs:pattern value='[^\s/\\:*?"&lt;>|]+' />
 		</xs:restriction>
 	</xs:simpleType>
@@ -592,4 +599,6 @@
 						<!-- The name of the imagery source -->
 						<xs:element name="name" minOccurs="1" maxOccurs="1" type="xs:string" />
+						<!-- A unique id for the imagery source -->
+						<xs:element name="id" minOccurs="0" maxOccurs="1" type="tns:id" />
 						<!-- The type. Can be tms, wms and html. In addition, there are the special types bing and scanex 
 							with hardcoded behaviour. -->