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.