When looking for the population of a community, it is important to consider the size of the census block group. Census block groups can vary considerably in size, and the U.S. Census Bureau does its best to keep the number of households within each one consistent. However, the number of people and households living in a block can be very different, resulting in wide variations in geographical size. For this reason, it is important to plan for density in cities that are expected to have high employment rates.