http://wiki.openstreetmap.org/wiki/Tag:waterway%3Dwaterfall
http://wiki.openstreetmap.org/wiki/Proposed_features/Waterfall
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HB: I'm not sure what the x,y offsets are all about. y=2,x=1 in the data for all features.
* edit by hand to force direction of flow to be downhill after uploading.
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HB: mainland UPLOADED 2010-11-25 in changeset 6452412
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HB 22 Aug 2012: checked for new dataset, updated field name.