Question: What new thing did you learn about latitude?  If you were already familiar with the concept, what are some of things you find interesting about its concept and use?

I've always known about longitude and latitude and how these imaginary lines help measure the distance and location's on Earth. But there are things I never really fathomed, like why or how latitude lines are in particular only 90^o rather than the 180^o like with longitude lines, which makes more sense because 180^o W+ 180^o E equals the usual 360^o that a complete circle makes. So how would latitude lines only be measured as being 90^o N and S for two different hemispheres as a complete measurement of the Earth? Circles are 360^o, as in an angle. Is it because of map projections or is the Earth really not a perfect circle - I don't get it.