The author of The Ghost Map, Steven Johnson, is a popular speaker as well as a writer. He's the host of the PBS television series How We Got to Now, in which he examines simple phenomena that have shaped the course of the 21st century.
I mention this because the best summaries you can find on The Ghost Map come from the author himself.
Here's a link to a 2006 TED (A Technology, Entertainment, and Design conference) presentation given by the author about the book: Steven Johnson: A Guided Tour of The Ghost Map. The video is roughly 11 minutes.
Also, a more thorough examination of the material from the book can be found in this recording of a talk Johnson gave at Google in 2007: The Ghost Map - Talks at Google. This video is nearly an hour in length.
Johnson also discusses the story from the book in the television program How We Got to Now, though the show can only be accessed online through Netflix.