If I were in your shoes, I would define it by how frequently I visit it, and how much care I put into it. It could be anything! I think every zone can be appropriate to use as an interface with a community.
I live in a city on 1/5th of an acre, and I define my permaculture zones based on how often I visit them and how much time I put into them. For me, this loosely shakes out to:
In summer:
Zone 1: Whichever part of my garden is currently growing seeds I'm trying to germinate or mature plants ready to harvest.
Zone 2: The rest of my garden.
Zone 3: My front yard, which is xeriscaped with fruit trees.
Zone 4: My lawn. I mostly ignore it, except when I chop it to use as mulch. I also pull out anything thorny or bindweed. I don't water it or mow it, and I welcome as many pleasant-to-walk-on, non-invasive species as want to grow in it.
Zone 5: Public parks.
In winter:
Zone 1: The plants inside under my grow light.
Zone 2: The plants under a greenhouse near my front door.
Zone 3: Any plants under a greenhouse further away than that.
Zone 4: Overwintering plants that have no winter protection.
Zone 5: Sidewalks that I know I'll have to shovel if the snow gets really deep.