I appreciate the suggestion! For what it is worth, the example cited above validates against that schema, according to this NIST tool (Xerces/Jing parsers). But I guess technically valid is not enough to get it to play nice with mapper. As mentioned above, I finally got Mapper to accept the POIs by simplifying the <gpx> opening tag to "<gpx>" and removing the "<metadata>" tag and data altogether. It's just the category issue at this point . . .