Write a question about the following article: As of the census of 2000, there were 478,403 people,  190,638  households, and 111,904  families residing in the city. The population density was . There were 215,856 housing units at an average density of . The racial makeup of the city was 51.0% African American, 41.5% White American, 0.3% Native American, 1.3% Asian American, 0.0% Pacific Islander American, 3.6% from other races, and 2.2% from Multiracial American. Hispanic or Latino Americans of any race were 7.3% of the population. Ancestry (United States Census) include German Americans (15.2%), Irish American (10.9%), English American (8.7%), Italian American (5.6%), Polish American (3.2%), and French American (3.0%). Out of the total population, 4.5% were foreign born; of which 41.2% were born in Europe, 29.1% Asia, 22.4% Latin American, 5.0% Africa, and 1.9% Northern America.

Question about the article:
How many more housing units are there than households?