Social Media Landscape

One term I hear a lot lately is "social media". From what I understand marketing people use this term to describe "everything but classic advertising in the internet". One big problem I have with the term and the discussion around it is that people use it in various contexts describing various aspects of it and making it look like "the big picture". In my opinion "social media" can't be understand as one big thing (like "mass media") working in one certain way with one set of rules.

I rather see a "Social Media Landscape" of various tools, ways to share or publish, connect and interact. And from what I see the rules differ between the areas in this landscape. But you can't adapt to the rules for this area when you don't know where you are. So lets start by looking at what this landscape looks like as of today.