New Ways to Read the Economy

SAN FRANCISCO—When the city's top economist needs a rough prediction of sales tax revenues, he watches the number of subway passengers emerging from the Powell Street Station on Saturdays.
Ted Egan, chief economist in the San Francisco Controller's Office, said he could wait six months for California to release the detailed sales-tax data he needs for city revenue projections. But it's quicker to look at passenger tallies from the station closest to the Union Square shopping district, which generates roughly 10% of the city's sales-tax revenue. The Bay Area Rapid Transit District releases the data within three days, he said: "Why should I have to wait?" Mr. Egan is among a growing number of economists and urban planners who scour for economic clues in unconventional urban data—oddball measures of how people are moving, spending and working.