“Seattle is at 47 degrees latitude”, the number of degrees is part of the complement.
In (2), "degrees" is simply a plural quantity.
(1) is familiar to me because earlier I encountered similar collocations (e.g. two car garage, three family house). But I'm very surprised at (2) and still can't understand it. Maybe to better my understanding, I need to consider the next sentences:It's at 47 degrees latitude
4 is wrong. A latitude is not an angle, it's a notional line parallel to the equator which is defined by an angle. A latitude of 47 degrees is defined by a 47-degree angle between the plane of the equator and a line drawn from the centre of the earth to a point on the planet's surface.What's the difference between (3) and (4)?
... and illustrated with new examples in #7Degrees are a bad example to explain this. What governs whether a noun of this kind is normally singular or plural depends on whether it’s being used attributively (before what it describes) or predicatively (after what it describes), as I mentioned in #2.
It is not correct in the sentence "It is 47 degrees latitude" nor in the sentence "It is 47 degrees temperature".If "47 degrees latitude" is correct,
thegoodscentscompany.com: Melting Point: 47.00 to 48.00 °C.Tricosane melts at 47 degrees temperature.
Tricosane melts at 48 to 54 degrees [...].