There are many conventions for describing points on a sphere. For example, does latitude zero refer to the North Pole or the equator? Mathematicians tend to prefer the former and geoscientists the latter. There are also varying conventions for longitude.
Volker Michel describes this clash of conventions colorfully in his book on constructive approximation.
Many mathematicians have faced weird jigsaw puzzles with misplaced continents after using a data set from a geoscientist. If you ever get such figures, too, or if you are, for example, desperately searching South America in a data set but cannot find it, remember the remark you have just read to solve your problem.
What’s the convention that says the North Pole has an angle of 0? In the standard calculus image of a sphere being swept out by a constant radius as theta varies from 0 to 2pi and phi varies from -pi to +pi, latitude 0 is indeed the equator.
Many options are available, but the convention that I used in calculus as well as the one used by wikipedia and apparently ISO (as stated in here: http://www4.ncsu.edu/~jwilson/files/mathsigns.pdf) is that phi varies from 0 to pi. Both are certainly used, but 0 north pole seems pretty standard.