This week's announcements about population growth and parks in Minneapolis and St. Paul seemed twinned. But actually the news of the central cities' increasing population, and that they have the nation's best park systems, was separate. And yet there seems to be a correlation — and maybe even causation — between the two.

That's because parks are one of those hard-to-quantify, yet crucial, "quality-of-life" features that matter to those choosing where to live. That's especially true for millennials, the younger cohort so important to attract and retain to keep regional companies — and communities — vital.

Minneapolis tied St. Paul for first place on the Trust for Public Land's 2015 ParkScore Index, which is based on metrics involving park access, park funding, and park facilities and investment. It's the third year running for Minneapolis as the nation's leader. And while it's the first for St. Paul, that's probably only because it's the city's first year of eligibility (the index was expanded this year to include the country's 75 most-populous cities, up from 60 in previous years). The achievement is remarkable in its own right, and especially considering the competition: Both beat out vaunted park systems in Washington, D.C. (third), San Francisco (fourth), New York (fifth) and Portland, Ore. (sixth).

Based on the rankings (and crowded running and biking trails, even in the winter), city residents, as well as those in surrounding suburbs, clearly value their parks. And, increasingly, they value the central cities themselves. For the first time since the 1970s, St. Paul is nearing 300,000 residents, after growing 4.4 percent from 2010 to 2014, according to estimates from the U.S. Census Bureau. During the same span, Minneapolis grew at an even greater rate, 6.4 percent, to top 407,000 residents. Both outpaced the region, which grew at a healthy 4.4 percent rate. Several suburbs grew at quick clips, too, no doubt in part because of the job opportunities available in the thriving downtowns.

Of course, both Minneapolis and St. Paul, like nearly all U.S. central cities, still face significant challenges. But unlike recent decades, population loss is not exacerbating them. There are several factors, and several leaders, contributing to this welcome population growth, but no doubt the world-class park systems were a contributing factor that led more Minnesotans to call Minneapolis and St. Paul home.