Hemisphere is a half of a sphere, typically we speak about northern and southern hemispheres in context such as the winter and summer being flipped depending on the hemisphere, or the Coriolis Effect etc. At first I thought you refer to America as a hemisphere, because you could divide Earth into two such hemispheres, sharing poles, that one of them is dominated by Americas (land-wise). But then you say "Columbia is also a term to refer to this hemisphere" and I'm lost. I googled "Columbia hemispheres" and couldn't find anything interesting.