I've decided to update my article on Understanding the BizTalk Mapper for BizTalk 2013R2. You can download the article here (in .docx and .pdf formats)
I originally wrote this article in 2008, and it was aimed at BizTalk 2006 R2. Since then, we’ve had 3 more versions of BizTalk: 2010, 2013, and 2013R2. With BizTalk 2016 entering CTP in the next few days, I thought it was time to revisit this article and update it for the latest (public) version of BizTalk.