See http://www.geonames.org/export/ws-overview.html for a full description of valid arguments and return values
GNchildren(geonameId, ...)GNhierarchy(geonameId, ...)
GNsiblings(geonameId, ...)
GNneighbours(geonameId, ...)
a geonames ID value
other parameters to pass to geonames
API doc for GNchildren is at http://www.geonames.org/export/place-hierarchy.html#children
API doc for GNhierarchy is at http://www.geonames.org/export/place-hierarchy.html#hierarchy
API doc for GNsiblings is at http://www.geonames.org/export/place-hierarchy.html#siblings
API doc for GNneighbours is at http://www.geonames.org/export/place-hierarchy.html#neighbours