I can't seem to understand this map. It seems too blurred and comfusing.
Swadian, this type of visualizations are not real "maps" as such, it is more of a graphical representation of trends.
In this case,
Foursquare is a mobile application that let's people "check-in" at different places so that they can share with their friends where they are. This map takes information from people's "check-ins" and puts it on a map. For example, if one day morning I check-in on Foursquare at San Francisco Airport and then in the evening I check-in on Foursquare at New York JFK airport, it is a good indication that I flew from SFO to JFK, so this graphic shows that as a blue line from SFO to JFK. Repeat this for thousands of users doing such "check ins" and you get a maze of lines joining places that people are traveling to. More people traveling between two points, thicker (brighter) the lines. Now look at the map again. You will see lots of red lines in NE corridor and California corridor and lots of blue lines elsewhere, shows the trend that a lot of people are taking the train in NE while a lot more are flying elsewhere.
This covers only Foursquare users so isn't very accurate. I am very social media savvy but I hate Foursquare and never use it because I do not see the point of the app except telling all day long "I am here" "I am here" "I am here". And I am not alone. All of my friends (20-somethings) who are big users of Facebook, Twitter etc also aren't Foursquare users. Now if this included data from Facebook check-ins, it would be lot more accurate of more broader public behavior.