Think of the Census 2000 summary files (SF1 through SF4) as a choir that sings the story of your community.
The full choir is SF1, all the voices in simple melodies. SF3 is smaller, chosen from the full choir to simplify the director's task of blending representative voices in more complex melodies.
By design, some voices emerge at times from each choir to sing solo, or in counterpoint. These are the separate tabulations by race and Hispanic ethnicity. Their stories ring clearly.
But we know the choir has more distinct voices embedded in its harmony. If we could hear them alone, we could hear their stories clearly. We could even hear the subtle differences between the melodies of Welsh and Scots, Kiowa and Comanche, Bulgarians and Romanians, Lebanese and Syrians.
Hence SF2 and SF4. In these files, each voice can emerge to sing solo. Are you a good enough director to lead them?