S.F.: Inspired Dashiell Hammett's detective novels (including "The Maltese Falcon"), Douglass Cross (who wrote the lyrics to "I Left My Heart . . . "), and many classic-rock performers, including the Grateful Dead, Jefferson Airplane, Janis Joplin and Santana. At the movies, it was the set for "Dirty Harry," "Bullitt" and "Milk." On television, "The Streets of San Francisco" lingers in memory.
The college crowd
S.D.: The U.S. Census said that, in 2008, 40.7% of residents 25 or older had bachelor's degrees. San Diego State counts about 27,500 undergrads; UC San Diego counts about 22,500 and University of San Diego (a private Catholic university) counts about 5,100.
S.F.: The U.S. Census reported that, in 2008, 50.3% of residents 25 or older had bachelor's degrees. San Francisco State reports about 24,000 undergrads, UC San Francisco reports none (its more than 4,000 students are all grad students in medical subjects) and University of San Francisco (a private Catholic university) counts about 5,500.
The international crowd
S.D.: 25.5% foreign-born, by count of U.S. Census, 2008.
S.F.: 35.6% foreign-born, by count of U.S. Census, 2008.
The LGB crowd
S.D.: It's not just the Hillcrest area. One UCLA study in 2006 estimated gays, lesbians and bisexuals amounted to 6.8% of the city's population (source: the Williams Institute on Sexual Orientation Law and Public Policy, UCLA School of Law).
S.F.: It's not just the Castro. That 2006 UCLA study estimated that gays, lesbians and bisexuals amounted to 15.4% of the city's population.
What travelers say
S.D.: Eighth place in the 2009 Condé Nast Traveler's Reader's Choice Award for favorite U.S. city, just behind Savannah, Ga., just ahead of Boston. Facebook travel fans as of mid-January: 56,858.
S.F.: Winner of 2009 Condé Nast Traveler's Reader's Choice Award for favorite city in the U.S. Facebook travel fans as of mid-January: 123,908.
What travelers do
S.D.: In 2008, the county hosted 15.2 million overnight visitors and 15.9 million more day-trippers.
S.F.: In 2008, the city/county hosted 5.93 million overnight visitors and 10.5 million more day-trippers.
Weather
S.D.: San Diego's average high, year-round: 71. Average low: 57. About 9 to 10 inches of rain yearly. Yet locals know to expect June gloom. By one analysis of weather since the 1950s, May and June are the cloudiest months of the year.
S.F.: San Francisco's average high is 63, the average low 51. About 20 inches of rain yearly.
Crime
S.D.: The FBI's 2008 uniform crime report shows 6,047 violent crimes and 40,365 property crimes among 1.3 million residents.
S.F.: The FBI's 2008 uniform crime report shows 6,744 violent crimes and 36,301 property crimes among about three-quarters of a million residents.
The conventioneer factor
S.D.: Down south, 2010's three biggest conventions will be the annual Comic-Con July 22-25; ASR Trade Expo, an Aug. 14-16 gathering of sports apparel retailers (20,000 expected); and the Society for Neuroscience, Nov. 13-17 (36,000 expected).
S.F.: To the north, there's Oracle OpenWorld, Sept. 19-23; Semicon West for semiconductor equipment and materials people, July 13-15 (25,000 expected); and the Winter Fancy Food Show of the National Assn. for the Specialty Food Trade, Jan. 17-19 (19,000 expected).
Politics
S.D.: Once, this was Nixon country. But in 2008, San Diego County voted 54% to 44% for Obama-Biden over McCain-Palin. In fact, with its larger population, San Diego County delivered more than twice as many Obama votes as San Francisco County.
S.F.: Liberal nirvana. Barack Obama got 84% of presidential voters in 2008.
Lay of the land
S.D.: 1,256,951 residents (and growing) in the city's 324 square miles, said the U.S. Census Bureau in 2006. That's more than 3,800 people per square mile. (Countywide census figures from 2008 show 3,001,072 people in about 4,200 square miles.)
S.F.: 744,041 residents (and shrinking) in 46 square miles, said the U.S. Census Bureau in 2006. That's more than 16,000 people per square mile. (The city and county of San Francisco share boundaries.)
Hotels
S.D.: In the city, 225 hotels and 37,425 rooms, by count of hotel trade analyst STR. In the first 11 months of 2009, the average room rate was $130.97.
S.F.: In the city, 226 hotels and 34,417 rooms, by count of hotel trade analyst STR. In the first 11 months of 2009, the average room rate was $147.46.
What's this on my hotel bill?
S.D.: Hotel tax is 10.5% if you're in a lodging with fewer than 70 rooms, or 12.5% if you're in a city hotel that's larger.
S.F.: Taken together, hotel taxes and a new "assessment" add up to 15% or 15.5%, depending on location.
What's that out in the water?
S.D.: On Coronado (an isthmus, not an island), a grand old hotel has held hundreds of guests at a time since the late 19th century. Annual number of tourists: more than 2 million.
