Think of it this way: if Google Maps and Flickr "knew" each other in the Biblical sense (as far as apps can, anyway), this is what their baby would be like.In our opinion, the popularity of Second Life tells us overwhelmingly that an invented reality may be much preferred to the, well, real reality. And even if that's not true, a virtual world is darn titillating.Semapedia, however, is a service built on the idea people want to join their physical and virtual worlds. And doing so has been made surprisingly convenient by Semapedia's take on tag. Semapedia Tags are mobile-friendly hyperlinks to online content from Wikipedia or any of its Wiki-oriented services: Wikinews, Wikiquotes, Wikibooks and Wikisource. The idea is to link from a physical place or object to relevant online content.It's also mash-up friendly with other (tired sigh) Web 2.0 offerings.The instructions seem simple enough. Image users enter their Wiki-whichever URL into the Semapedia tag-builder, which builds a PDF file -- called a custom bar code for these purposes.You download and print the bar code (best to do it on self-adhesive paper, says ContentWrangler) and stick the tags to the object or location.The bar code is well labeled: "Hey! This is a physical hyperlink to Wikipedia. Please scan the code or enter the URL on your phone." It would be neat if the service grew so popular that people would recognize on-the-fly what the code was. Maybe one day. Anyway, passersby can use their mobile phones to read the tag and gain access to the embedded information on the Internet.This could make an excellent brand-based guerilla campaign, provided it's well-executed. The tags can also be embedded into document content.The Semapedia blog has some information about what they do, and their new Chinese offering. There are also some neat illustrations of the bar codes. Read up, then buy labeling sheets and wild out.