It is Iran accounts with 95% of the worlds production Spain only produces 300 kg. India, Greece, Azerbaijan, Morocco and Afghanistan produce most of the rest (in that order).
Saffron is the dried stigmas from the flower of the saffron crocus, which is itself derived from its wild "parent" plant. As just the stigmas of the flower are used, and they are small, it makes sense that a lot of them are required to produce even a few grams of this, the world's most expensive spice.
Wikipedia has additional information, and you'll find a link below to their wonderful post on this ancient spice. Why not surf on over and check it out? You're just a click away from some insight into something that dates back to prehistoric times