A few days ago, I published an interactive map of American migration on Forbes.com. Since then, it’s become more popular than I could have possibly imagined. It’s been shared 5,000 times on Facebook and written about by The Economist, three different Atlantic blogs, three different New York Times blogs, and basically the entire “-ist” franchise (Gothamist, Chicagoist, DCist, and so on)–plus 1,700 other blogs and publications of various sorts. It’s broken Forbes‘s record for interactive content. To say I’m grateful for the reception would be a profound understatement.

Part of the reason that readers have enjoyed the map, I think, is that it confirms graphically what people have long known or suspected about regional trends based on either hard statistics or gut feelings: that the Pacific Northwest is being flooded with Californians, that Florida is suffering from brain drain, that Los Angeles no longer has the universal draw that it had during much of the 20th century, and that Detroit is in serious trouble and Dallas is doing rather well for itself.

At a higher level, the map confirms that the United States is a highly mobile country: one in which the lack of jobs in Detroit and the surfeit of them in Dallas draws massive numbers of people (806 of them, in fact, moved to the Dallas region from Wayne County; 167 went the other way). Commentators have offered theories of how taxes, costs of living, and quality of life create patterns on this map as well. Americans know what they like, and they’ll move to get it.

In skimming through the astonishing number of comments that people have posted (mostly to sites other than Forbes.com), I’ve come across a few persistent questions that I’ll answer here before explaining how the map works. READ MORE >

Forbes published my new map of Chinese overseas investments last night, and I’ve been pleased with its reception so far. It’s the first map I’ve made that involves animation, and it’s also the first map that I’ve built from scratch using nothing but ActionScript and Python. That turned out to be tricky in a neat, hackerish sort of way.

In the past, I’ve made all of my interactive maps using Avenza’s excellent MAPublisher software. MAPublisher handles geocoding and projections, which leaves me free to faff about with color schemes and callouts.

When you code your own map from scratch like this, though, you have to write something to geocode points and then project them (unless you’re partial to maps where Canada, Greenland and Russia seem to be taking over the world). There are less math-intensive solutions to this, like creating a map in Illustrator and then moving it to Flash (recommended for choropleth maps), but I wanted maximum programmatic control over the map (and the thrill of coding my own solution).

Geocoding was fairly easy in this case; I just derived centroids for each country using ArcGIS and merged those coordinates into the dataset from Heritage’s Derek Scissors using Stata. The data for each country now included deal value, acquirer, target, target’s country, latitude, and longitude.

Now for the projection: simply sizing down the latitude and longitude coordinates linearly by enough to make them represent pixel locations would result in a so-called ‘unprojected’ map that’s a dishonest representation of shapes and relative sizes. Unprojected maps also tend to waste a great deal of space by making the highest and lowest latitudes enormous and the middle latitudes small–a general problem for Web layouts like ours, where maps can’t be more than 768 pixels wide, and for this map specifically, because a great deal of Chinese investment has taken place in parts of Africa and South Asia that are near the equator. READ MORE >