People are particular about the forms of communication they employ when expressing themselves, through social networks or any other media, because different forms possess different powers of conveying information.
When in the physical presence of others, we can communicate verbally, visually or tactilely with our words, gestures or touch. Words are usually chosen to communicate abstract concepts, finger pointing is best suited to convey direction, and hugs provide the quickest route to imparting fondness.
When afar, we can send each other letters, speak to each other over the phone or route a message through a friend. The message might ostensibly be the same despite the form it takes, but a letter will likely impress a greater sense of consideration, a phone call will impart nuances by way of intonation, and a routed message will include the implicit validation of its intermediary. The transmitter must choose their form carefully if they want to get the intended message across because each form has its own abilities and disabilities to deliver information.
Likewise, social networks are constructed around particular forms of communication and consequently limited to the characteristics of those forms. The various forms can be considered types of content, because shared information persists within a given network and is intended to benefit its consumers by entertaining or edifying them. As such, it's important to consider the types of content people can share within a network as key to its communicative value.
All social networks collect identification information from their members and publish it back out as static content. Usually this consists of a member's name and portrait as well as their location and one-line biography. Particularly identity-centric networks collect a lot more static, or evergreen, information such as employment and educational history, music and movie interests, and contact details. The sum of this content is displayed primarily on a single page, which serves to anchor the user's identity within a network and provide a reference point to others. Therefore, networks share the profile as a fundamental content type.
Social networks almost universally publish some manner of relationship content, too. Friendships, follows, subscriptions, and the like indicate that pairs of people have a relationship between each other that's worth recording and making known. And the types of relationships that can be captured depend on the model a given network has implemented and how that model has been communicated throughout the service. This content – which is often showcased on profile pages but importantly delivered through notifications as well – constitutes yet another fundamental type that varies only in implementation.
The content differences between social networks, however, mainly come from the types of information that users are able and encouraged to submit as discrete objects. These types are manifold: photos, videos, graphics, status updates, blog posts, articles, documents, books, events, travel plans, travel advice, questions, answers, bookmarks, pokes, reviews, deals, goods for sale, money, vital stats, purchases, gadgets, badges, check-ins, short-form messages, gifts, songs, audio clips, polls, webpages, brands, applications and more. This content is posted proactively by users and its immediate destination is often a feed or profile page. It will likely be repurposed for other consumption points, such as search or syndication, too.
There is also a host of reactive content types that social networks variably support. These include, most commonly, comments or replies and gestures that indicate approval or disapproval of shared content, such as likes, reposts, favorites or votes. These reactive types are designed to permit direct interaction around pieces of content, allowing the publisher and any other established participant to garner feedback and increase the impact of their contributions. Furthermore, reactive content can be generated in response to other reactive content, thereby extending chains of interaction to deeper levels.
Some social networks support many of these proactive and reactive content types while others specialize in just one or a few. Support may also differ in subtle yet important ways between two or more networks, allowing those networks to convey substantially different information and consequently present dramatically different value propositions to their members.
Comparisons aside, every network must be designed around a combination of content types that can be used to fulfill the identifiable communication needs of its producers and consumers. On one side of the equation, a sufficient number of people must be interested in producing a given type of content because it allows them to express themselves in a way they find valuable. On the other, a sufficient (and most likely larger) number of people must be interested in consuming that content because it benefits them in a recognizable way.
Social network designers must identify not only certain communication needs and their corresponding content types but the frequency and size of those needs as well. Network participation requires commitment on the part of its members, lest they forget or resist leveraging it when their needs arise. And the only way to earn that commitment is to satisfy members' content needs either frequently in small ways or occasionally in big ways.