From Social Patterns
Networked publics are publics that are restructured by networked technologies. As such, they are simultaneously (1) the space constructed through networked technologies and (2) the imagined community that emerges as a result of the intersection of people, technology, and practice. Social network sites like MySpace and Facebook are networked publics, just like parks and other outdoor spaces can be understood as publics. Collections of people connected through networked technologies like “the blogosphere” are publics, just like those connected by geography or identity are.
The concept of networked publics is slippery because the concept of “publics” is messy. The term “public” is contested, has multiple meanings, and is used across disciplines to signal different concepts. During my interviews, I found that teens also struggle to define this term and rely on multiple meanings to approach a definition from different angles. When used descriptively, “public” is often in opposition to the equally slippery concept “private” to signal potential access.
--both quotations, danah boyd, "Taken Out of Context: American Teen Sociality in Networked Publics"
When designing a social application of any kind, you must immediately grapple with the perspectives of - at the very least - two publics. One is the "whole world" that will have some way of glimpsing your site, if only to see the high walls of your private garden. The other is the networked public you hope to cultivate, composed of the body of all of your site's members and participants. Most likely there will be more than two. The outside world may itself have sub-publics that view your site from without in different ways. More importantly as your members meet each other and organize themselves into groups around common interests, there will start to be multiple networked publics within (or, really, facilitated by) your system.
Thus, when your users engage in Public Sharing through your application, this may mean they are sharing objects with the whole world (as when someone posts content to an ordinary blog), or with the entire membership of your site, or with some other designated public they relate to through your site.
Alternatively, those choices may be baked into the rules of the system, so - for example - when choosing to share an object at Facebook, one choice is to add it to your profile:
When an object is shared by posting it to one's profile, the rules for who can see at are inherited from the rules of the profile and the account, not set manually at the point of sharing.
- Digital Publics, Conversation and Twitter (Kevin Marks in his blog, Epeus' Epigone)