RJMetrics, the Philadelphia-based online-analytics firm, offers a crude but intriguing test for flagging the busiest tech-startup hotbeds: Founder Robert J. Moore has posted this report (link fixed) ranking local utilization of Meetup, which calls itself "the world's largest network of local groups" (and which Moore says has become a "geek elite" online super-community, with 3.7 million members in more than 16,000 tech-themed Meetup groups) as a proxy to estimate the number and vigor of local tech startups-in-progress.

The report joins data from Meetup's application-programming interface (API) to list U.S. and foreign cities by four combined measures of Meetup use: local membership; market penetration; number of local groups using the service; growth rate.

The top U.S. cities are the usual tech and investor hotbeds: San Francisco, New York, Seattle, Washington DC, Austin, Boston. But Philadelphia punches way below its weight: the 5th-largest U.S. city ranks only 19th on the combined Meetup scale. Smaller places like Atlanta, Minneapolis, Boulder and (separately) Denver, Colo., and Portland, Ore., rank higher. Even Pittsburgh isn't far behind (#23). (Foreign cities including London, Toronto, Tel Aviv are also big concentrations of Meetup users, as are European capitals; India's and Singapore's English-friendly tech centers; and Australia's cities.)

Can't accuse Moore, a Glassboro native and Princeton grad who started the company in his family's Collingswood garage and moved it to Camden before expanding into Center City, of hometown bias.

It's a bit more the reverse: Moore admits this is a "strictly quantitative analysis" that doesn't attempt to calculate "social and economic" factors. For example, he told me, "Philly has strong medical and pharma tech sectors that likely aren't well-represented" because their workers, well, don't use Meetup the way software and Internet companies do. (One might say the same of the great China and Japan cities, which aren't on RJMetrics' international Top 20 Meetup list -- while Auckland and Brisbane are.)

Speaking for his RJMetrics team, "there is nowhere in the world we'd rather start or build a business today" than Philadelphia, Moore added. "We are confident Philadelphia will climb this list as years pass."