If it seems a little crowded on weekdays in cities like Washington, D.C.; Irvine, Calif.; Salt Lake City, Utah; or Orlando, Fla.; it’s not your imagination. Among cities with 100,000 or more people, these four show the highest percentage increases in population during the day as opposed to their resident population.

     The findings come from the first-ever U.S. Census Bureau estimates of the daytime population for all counties and more than 6,400 places across the country, based on Census 2000 data.

      The concept of the daytime population refers to the number of people, including workers, who are present in an area during normal business hours, in contrast to the resident population present during the evening and nighttime hours.

      “Information on the expansion or contraction experienced by different communities between nighttime and daytime is important for many planning purposes, including those dealing with transportation and disaster relief operations,” said Census Bureau Director Louis Kincannon. “By providing information on the number of people not living in the area, but nevertheless greatly affected by the event, the data can provide a clearer picture of the effects of disasters such as Hurricanes Katrina and Rita.”

     The places where the largest percent increases in daytime over nighttime populations occur tend to be those with small resident populations. For example, among medium-sized cities, Greenville, S.C., has a daytime population that is 97 percent higher than its nighttime population. Palo Alto, Calif., increases by about 81 percent, and Troy, Mich., by 79 percent. Among very small places, gains approached 300 percent in Tysons Corner, Va. (292 percent); and El Segundo, Calif. (288 percent). (See Table 1.)

Other highlights:

• New York City has the largest estimated daytime population, at more than 8.5 million persons. The increase of more than half a million people over the nighttime population is bigger than that found in any other area. However, the 7 percent increase puts New York in the middle of the pack on percentage change among cities with more than a million residents.
  
  
• The second highest numeric daytime increase is in Washington, D.C., where 410,000 workers boost the capital’s population by 72 percent during normal business hours.
  
  
• Other big cities with large daytime gains are Atlanta (62 percent), Tampa (48 percent) and Pittsburgh and Boston (both around 41 percent).
  
  
• Typical examples of sizable expansion of daytime populations in small cities can be found in places such as Paramus, N.J.; Redmond, Wash.; and Beverly Hills, Calif., among others.
  
  
• About 250,000 people worked in New Orleans prior to Hurricane Katrina. Almost 150,000 of these workers were residents of New Orleans, but the remaining 100,000 lived outside the city.
  
  
• One of the most extreme examples of daytime population increase is Lake Buena Vista, Fla., which has almost no permanent residents but swells to an employment center of more than 30,000 people during the day.

     Additional tables are available on the Census Bureau’s Internet site at <http://www.census.gov>. Choose the “Subjects A to Z” link at the top of the page, click on the letter “D” and then select the link to “Daytime Population.”

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The estimates are based on Census 2000 sample data. For information on confidentiality protection, sampling error, nonsampling error, definitions and count corrections, see <http://factfinder.census.gov/home/en/datanotes/expsf3.htm>.