Whatever you think of the politics, and whatever happens in the days to come, give Occupy San Francisco credit for this: It has activated a park that sat dormant for 10 years.

The ragtag ensemble of tents and tables, political art and communal blankets also is living proof that in the long run, urban spaces take on a life of their own.

The encampment - sorry Mayor Lee, but that's what it is - fills a grassy rectangle south of Justin Herman Plaza along the Embarcadero. It includes a raised palm-lined walkway facing the Ferry Building and is named after union organizer Harry Bridges, who surely is smiling down on its politicized current state.

The space opened in 2000 on land vacant since the removal of the elevated Embarcadero Freeway in 1991. From then until now it has been a primly designed place apart, filling up only when a marathon or some other event needs support space.

People had ideas but the ideas did not take.

The first one explains the lawn: It was intended as a forecourt to a restored bit of Old San Francisco, a majestic pipe organ from the 1915 Panama-Pacific International Exposition. The notion had more fans than funds. The concrete clearing that was to hold the organ remains bare.

Ten years later, well-connected men friendly with Mayor Gavin Newsom looked at the empty lawn and thought - bocce courts! Well-connected companies chipped in materials and assistance and two courts premiered in November. Popular after work, perhaps, but the space remained as barren as ever during the day.

Signs of an upbeat village

Then the Occupy San Francisco movement arrived a little more than two weeks ago.

I don't want to glorify the stature of what now includes more than 100 tents and canopies. The city had to deal with overflowing portable toilets Sunday morning. When I walked through on Sunday afternoon, several earnest Occupiers were trying, without much success, to calm a woman loudly calling everyone around her a Nazi.

Visually, the clustered tents are as varied as the elements of the movement that set them up. For every poster or chalked slogan sticking to message - that 1 percent of people and corporations control a disproportionate share of power and wealth - others tout more generic causes of the left, such as the virtues of hemp.

But the Sunday visit also showed evidence of what so far feels like an upbeat, ad hoc village. Clusters of young adults sat on steps, killing time with amiable talk. Three people circulated picking up litter. Children in Halloween costumes worked on art projects while their parents looked on; the families had come from elsewhere in the city to show support.

Other than visibility, there's no site-specific reason to settle in the space. It's not politically charged, as is the case with Frank Ogawa Plaza outside Oakland City Hall. The campers in Harry Bridges Plaza are there because they filled a void.

Filling in the blanks

The only people who occupied this urban clearing in the past were homeless people - some perhaps now residing amid the would-be system-changers - who knew they could linger without being hassled.

To the south is the rump end of the Hotel Vitale, to the east a side view of the sterile slabs of the One Market office complex, and on the east the Embarcadero's multiple lanes of traffic. The streams of people along the north edge are streaming from Market Street to the Ferry Building or vice versa.

Now the lawn and walkway have been appropriated. Which is what tends to happen to ill-used open space in busy cities.

Look to the north, for instance, where Harry Bridges blurs into Justin Herman (exactly where, only a cartographer would know). The tents of campers give way to the tents of vendors who line up to catch the eye of souvenir-susceptible tourists. The brick hardscape beyond that is fenced off for the installation of its most popular annual feature, an ice-skating rink.

You can argue that the Occupy San Francisco encampment isn't legal. You can worry about sanitation conditions or future conflict. But what's happening before our eyes is an example of how cities never stand still - and often change in ways that no planner or politician can predict.