The Extinction map of Ark Survival Evolved has one basic area where you can find wild gigas, that are tamable. Where gigas spawn are where Carcharodontosaurus spawn too. The spawns are located around the out edge of the snow biome, not inside it. I have seen most of the at either end of the "smile", but they are said to be found all along that southern sweep of the snow biome.
|Ark Extinction Gigas are Located around the outer edge of the snow biome.
|Giga on Extinction