Complex sentence: According to a census survey done between 1990 and 2000, population growth was the greatest in the West (pop. rose 19.7%) and the weakest in the North-East (pop rose 5.5%) showing a westward migrating trend in the United States.
Split into simpler sentences: According to a census survey done between 1990 and 2000, population growth was the greatest in the West being as the population rose 19.7%. Population growth was the weakest in the North-East with a population that rose 5.5% showing a westward migrating trend in the United States.