Index: trunk/data/maps.xsd
===================================================================
--- trunk/data/maps.xsd	(revision 9593)
+++ trunk/data/maps.xsd	(revision 9610)
@@ -680,4 +680,11 @@
 								</xs:complexType>
 							</xs:element>
+							<!-- list of checksums, that indicate "no tile at this zoom level" situation -->
+							<xs:element name="no-tile-checksum" minOccurs="0" maxOccurs="unbounded">
+								<xs:complexType>
+									<xs:attribute name="type" type="xs:string" />
+									<xs:attribute name="value" type="xs:string" />
+								</xs:complexType>
+							</xs:element>
 							<!-- tile size provided by imagery source. Default - 256 -->
 							<xs:element name="tile-size" minOccurs="0" maxOccurs="1" type="xs:positiveInteger" />