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.

The lines obscure everything! Why not just use colored fills in the counties (i.e., a choropleth map or heat map) to illustrate net change?
Because that would be visually boring. The lines create a narrative by forcing the reader to see relationships between counties, not just flat characteristics. Click on Miami: your eye immediately catches the big swoosh of people from the Northeast and then follows its outward counterpart to the West. The lines are dynamic and directional; they suggest movement, which is exactly what the map is meant to show.

The other problem with the heatmap approach is that it would result in lots of emptiness: Maricopa County, Ariz. (which contains Phoenix) has the most connections of any county: 834. That’s a lot of lines on this map, but it’s not many counties to color: just over a quarter of the 3,000 or so counties on the map. Rather than seeing an explosion of movement when you click on Maricopa County, you’d see a limp, mostly-blank map with a few counties colored in and nothing to suggest their relationship to Maricopa County. That issue becomes really acute when you get to the 2,700 counties with fewer than 100 connections.

So there you go, Snoozy McBoringstein.

Well, then, have the lines appear by default but give me a button that I can use to make them disappear.
Okay, sure. I’ll try to satisfy these criticisms by way of more features in version 2 of the map, which I’ll probably publish this fall when the IRS’s 2009 data will be released. I thought of a lot of features that I’d like to include but couldn’t because this map already taxes most users’ computers. That can be fixed through careful optimization, but I didn’t have time to do as much of that as I’d have liked because I published the map literally 20 minutes before leaving for a week in Hong Kong.

This map is incomplete/misleading because the IRS data doesn’t include immigrants.
True, I suppose, but this is the very best migration data available and, in fact, its problems can be generalized beyond that complaint: the IRS migration stats don’t include anyone who didn’t file an income tax return (or count as an exemption on someone else’s return) in both 2007 and 2008. That means that there are some distortions when it comes to people entering the workforce (through immigration or by getting a first job) and people leaving it (i.e., retirees who file their last tax return the year that they move to Florida). It also probably leaves out some low-income earners who don’t file income tax returns at all.

How It Works

More than a few people (starting with @TribData) have asked how I built the map. Here’s the broad outline: IRS Data + Python + county shapefile + MAPublisher + ActionScript 3.0 = interactive map with tons of data.

I began with data from the Internal Revenue Service that reports migration stats for every county in the country: inward and outward tables that include number of returns filed, number of exemptions reported on those returns, and aggregate adjusted gross income for those returns. Using Python, I broke down the data and wrote 3,000 XML files (one for each county) plus a grand index file that contains county names and FIPS identifiers and uploaded all of those to our servers.

The map itself began with a county shapefile that I beautified with Avenza MAPublisher and imported to Flash using the process outlined on Kelso’s Corner. The result is a Flash file in which each county area and outline is its own movie clip, named with FIPS identifiers.

My ActionScript code in the map draws all of these together: it downloads the index XML file, then cycles through all of the county movie clips and adds event listeners for rollovers and clicks to each one (this is what it’s doing as the loading bar creeps across the page).

When the user rolls over a county, the rollover event listener fires, retrieves the county name from the index, and displays it. When the user clicks a county, the click event listener fires, downloads the relevant individual XML file, and draws lines between the clicked-on county and each associated county.

JavaScript in the article page looks for a URL parameter called “preload” and passes its value along to the Flash file; this allows users to share links that pre-load a particular county.

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.

I went for the Winkel Tripel projection, currently the presentation of choice for National Geographic and one that strikes a reasonable balance between angular and spatial distortion. Wikipedia conveniently provides the transformation formulae, which include functions like arccosines that I hadn’t seen since college physics classes. With longitude as λ, latitude as φ, and standard parallel–the latitude above and below the equator at which the projection is entirely accurate–as φ_1, we get mappings for the x and y coordinates thus:

where

It would be easy to code these equations into ActionScript and have each user’s Flash player map the investment dots on the fly. But Flash files with more than 200 event listeners (counting rollover and click listeners on the dots and bar graph and click listeners on the legend and buttons) already strain some feebler computers. Preprocessing the mapping seemed like the way to go, so I did the projection transformation in Python as I built the XML files that underlie the map (one file that includes every investment, its magnitude for sizing, its x/y coordinates for location, and details for the callouts; and another file that includes monthly data for the bar graph).

With the XML files built in Python, ActionScript just had to handle some simple placement and sizing tasks: creating a circular movie clip for each investment, coloring it appropriately, and adding it as a child to the stage. The script adds all of the circles to the stage when the map loads, during the time that the background displays a big “Loading…” notice; as the animation plays, the circle movie clips are set to visible and a little popping animation is applied along with a small sound effect. While the Flash file is open in the viewer’s browser, the circles and spark bars are stored in arrays for easy access with the .indexOf() method.

The combination of sound effects and spark bars might seem redundant, but they illustrate two different dimensions of these investments: the spark bars show dollar volume, which might be high even in months when there’s just one investment. The monthly number of investments is the other dimension: the visual animation is meant to call the viewer’s attention to each newly-appearing circle, but it’s difficult to keep track of every new dot on the map every month. The sound effects reinforce the visual animation by giving an overall feel for the number of dots added each month (the popping sound plays once for every new investment in each month).

Terminal 3, which opened in the 1960s as the Pan Am Worldport and managed to escape the following five decades with only minimal improvement, is now festooned with kite-like leak catchers and a complicated system (series?) of rubber tubes that divert rainwater from the terminal’s crumbling ceiling (a couple of them are shown in the photo below).

Terminal 2, which is connected to Delta’s other building by a sequence of broken moving walkways, has likewise avoided any major upgrades since it was built for some other long-defunct carrier in the middle of the last century (Eastern Airlines? I’m writing this on my phone from a worn seat in a threadbarely-carpeted waiting area, so research is difficult).

Over the last decade, JFK has gone through an impressive modernization process; the pleasant-enough Airtrain whisks me to the airport from the thrillingly-rebuilt Jamaica Station in less time than it takes a bored TSA agent to find a rogue yogurt container. The airport’s other terminals have been rebuilt: first the terminals that serve a motley assortment of foreign airlines, then American’s complex, and then JetBlue’s. If LOT Polish Airlines gets to use a terminal that’s not an embarrassment to New York City, why can’t one of the airport’s hub carriers (and now the largest airline in the world) have one that’s somewhere above Soviet bloc standards?

At the top of his results page are two news articles detailing his latest scandal (in which he apparently contacted a woman who lodged a domestic abuse complaint against his aide).

Below those news headlines are Paterson’s Wikipedia article, the last section of which documents his moribund gubernatorial campaign, and his state government website. Then come two headlines from the Huffington Post, one questioning whether Paterson will resign and another announcing the resignation of the aide involved in the domestic dispute.

Finally, right before Paterson’s campaign website comes a Business Insider article about the rumors that circulated in Albany over the New York Times’s investigation into the governor’s aides.

Things do not look good for David Paterson.

The data that the maps are based on come from my friends at Inrix, a clever company based just outside of Seattle that measures traffic congestion using data from GPS tracking systems in commercial fleets. I’ve written about them before, and used their data in December 2008 to form the Forbes “Chirp Index,” a group of leading indicators with which we (fairly accurately) predicted that the recession would bottom out late in the summer of 2009.

After a couple of years of declining traffic congestion (due first to rising gas prices and then to rising unemployment), traffic congestion seems to be coming back. Growth in economic activity and stimulus-related road construction projects are bringing more people onto the roads and then slowing them down.

A minor tiff erupted in the comments section of my article; one commenter suggested that traffic congestion wouldn’t come back if only we invested more in public transportation. The next commenter wrote that public transportation hasn’t been proven to have any meaningful impact on traffic congestion.

Both commenters make legitimate, though incomplete, points. Public transit advocates tend not to talk of payoffs from transit investment in terms of immediate relief from congestion; after all, much of the housing and commercial space that’s been built in this country over the last 50 years is fundamentally incompatible with efficient transit schemes. The office-park worker who lives on a cul-de-sac will likely never be able to use even the most ambitious new transit system to commute–at least not as long as he lives in a housing tract and works in an office park.

That’s why transit advocates concede that new rail lines won’t immediately cut traffic on adjacent arterial roads. Rather, they say, transit systems encourage the kind of development that is compatible with transit use: walkable neighborhoods with a combination of townhouses, apartment high-rises, offices and shopping that are based around transit stations.

This kind of development is popular in places like Northern Virginia, where a well-run rail system links outlying areas to a massive job center in Washington, D.C. It takes much more patience to introduce these kinds of transit-oriented neighborhoods to cities with comparatively weak central business districts, like Phoenix, Los Angeles, and Atlanta, since people who live in them but don’t work in them may still have to drive to otherwise-inaccessible office parks.

So new transit networks in car-oriented areas constitute major investments in reorienting urban development over a period of decades, not a quick attempt to remove a few cars from highways. Traffic will come back this year–there’s no way around that–but sound investments now could mean that it will bring fewer headaches fifty years from now.

Here’s how it works: copy and paste the code below into the HTML of your web site wherever you want it to appear. Because we’re bound by an embargo and are not allowed to release this year’s ads until the end of this year’s Super Bowl game, the viewer will contain ads from last year at first. Embed it anyway. In an unprecedented feat of Internet magic, the viewer that you put in your own blog will automatically replenish itself with fresh, fresh 2010 ads after the big game on February 7. Again, we make it easy for you.

When we switch in the new ads on the 7th, we’ll also remotely activate a voting feature in the viewer that will let readers pick the best and worst ads. Expect to generate some good discussion in your comments section.

Here’s the viewer. Scroll down to copy and paste the code.

And here’s the code:

<script type="text/javascript" src="http://images.forbes.com/scripts/swfobject.js">
</script>
<script type="text/javascript">
swfobject.embedSWF("http://images.forbes.com/jb/superbowl/viewer.swf",
"myAlternativeContent", "568", "600", "9.0.0", "expressInstall.swf", {},
{allowscriptaccess:"always", allownetworking:"external"},{});</script>
<div id="myAlternativeContent">You must have Adobe Flash Player 9
or higher installed to view this content
<a href="http://www.adobe.com/go/getflashplayer" target="_top">
<img border="0" alt="Get Adobe Flash player" align="left"
src="http://www.adobe.com/images/shared/download_buttons/get_flash_player.gif"/>
</a></div>

Visit Forbes.com for more details on our embeddable Super Bowl ad viewer.

The day that I took this walk, the south sidewalk was closed, so I used the walkway on the north side of the bridge. The natural scenery up the river is just as magnificent as the man-made scenery downriver.

From the metro area that gives us such names as Hoboken, Weehawken, Hackensack*, Harsimus Cove and Throgs Neck, comes Yonkers, which sits across the city line from the Bronx. It’s visible from the bridge.

The Cloisters, part of the Metropolitan Museum of Art, sits on the top of a hill in Fort Tryon Park at the very northern tip of Manhattan. Its tower pokes through the trees in this photo. Below it, just above the shoreline, is Robert Moses’s Henry Hudson Parkway. In The Power Broker, Robert Caro’s biography of Moses, the construction of the Henry Hudson Parkway was where Moses went from arrogant-but-generally-good to essentially maniacal (but there were signs earlier, of course).

The views of Midtown are as good as ever, of course. The scale of the Empire State Building is, I think, best appreciated from this distance, where it still overpowers just about everything else.

As we cross over the Manhattan shoreline on the bridge, we can see railroad tracks below us. These were originally built by the New York Central to gain access to the West Side (its Grand Central Terminal is on the East Side). Now they’re owned by Amtrak, which uses them for trains to Albany and Chicago. These tracks and the environment around them in the early 20th century inspired Robert Moses to pursue public works in the first place. When he built Riverside Park and the Henry Hudson Parkway, the tracks were the source of much of his funding, part of which came directly from the New York Central and another chunk of which came from Federal funds earmarked for the elimination of railroad grade crossings.

Upon arriving in Manhattan, we’re greeted by the sight of the George Washington Bridge Bus Terminal (in the foreground). Behind it are residential towers that are located directly on top of the Cross-Manhattan Expressway segment of I-95.

And now, a final view of the bridge.

The tour is over. The A train whisks me back downtown, and safely home to Park Slope.

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Fort Lee has a small-scale downtown area, complete with those indicators of prosperity, Starbucks and Borders. Many of the stores and restaurants serve the area’s large Korean population.

But in some sense the real center of Fort Lee shifted north after the George Washington Bridge was built and the convenience of driving across it was realized. Much of the city was built in what appears to have been one colossal belch of ill-considered, garage-based, post-war development.

But Fort Lee has one really, really huge thing going for it: Palisades Interstate Park stretches north from here, passing the New York state line. The southern tip of the park just south of the George Washington Bridge is called the Fort Lee Historic Park.

Entering the park from Fort Lee involves walking up a long set of stairs into a dark forest and emerging shortly to find a 1970s-style visitor center. It was here, the center explains, that George Washington defended the Hudson River (unsuccessfully) against the approaching British in 1776.

The museum includes everything you’d expect from a visitor center in a historic park, including lots of reproduction flags and big displays where small flashing lights show the positions of Washington’s troops. Classic.

Just a hundred yards or so beyond the visitor’s center, the woods open up and an overlook provides a spectacular view of the river, the bridge, and the city.

The Bridge’s sinewy construction is magnificently displayed from here. It was one of the first major works of Swiss engineer Othmar Ammann (whose last major bridge was the Verrazano-Narrows). The towers had been intended to be clad in stonework designed by Cass Gilbert, but cost considerations left the steelwork exposed.

Beneath the Manhattan tower is the lighthouse immortalized in Hildegarde Swift’s The Little Red Lighthouse and the Great Gray Bridge.

From here, we can see two more major bridges: on the left in the picture below is the superstructure for the Hell’s Gate Bridge, a railroad bridge said to be one of the strongest in the world, on which Othmar Amman did some engineering work. To the right are the towers of Robert Moses’s great Triborough Bridge.

From here it’s easy to get to the sidewalks across the bridge.

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The supermarket is at the center of a small strip-mall that also includes a Japanese bookstore and stationer. The books there are beautifully printed, and their uniform dimensions make for a pleasing display.

The magazine section has Japanese editions of American publications, as well as Japanese periodicals. Included is “Wink Up,” a teen magazine.

From behind Mitsuwa, we get a great view of Morningside Heights, the neighborhood that includes Columbia University’s main campus and Riverside Church (right), which was built by John D. Rockefeller from 1926 to 1930. Its congregation remains prominent today, and is particularly famous for its leftist activism. The tower of the church contains the only carillon in the world that bests that of my alma mater, the University of Chicago. Both instruments are named for Laura Spelman Rockefeller, the wife of John D.

The colonnaded rotunda on the left-hand side of the photo is the tomb of Ulysses S. “Bury me next to my wife, but nothing too fancy” Grant. It was finished in 1897, fell into disrepair in the 1970s along with much of the rest of public New York, and was restored impressively in the late 1990s.

Getting back on the bus, I keep heading north.

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Back between Jersey City and Hoboken, the light rail trains pass this stop, which really ought to be announced by a recorded pirate voice:

After leaving Hoboken Terminal, and just as they pull out of the Lincoln Harbor station, where I disembark, the light rail trains pass beneath the “Helix”, a curved causeway that brings Route 495 off of the Palisades and down into the Lincoln Tunnel. The views from the Helix are spectacular.

Lincoln Harbor is a drab, sterile development that includes a marina, a couple of strange housing/something-else piers, and a blue office complex that includes this gem of a food court:

But at least this is where the bus stops, and it’s on time. Route 158 follows River Road up the narrow plane between the Hudson and the Palisades. Good views of the west side of Midtown are off to the right the whole way:

The road has been developed quickly over the last few years, and there’s now a great deal of expensive, low-quality housing crammed in between it and the river.

Condos start at $600,000 in “Grandview II at Riverwalk”, and the developer, K. Hovnanian, promises “an enticing shopping promenade” in the neighborhood. But the commercial options in this area are bland strip malls like this one, which turns its back on Manhattan’s Upper West Side and the tower of Riverside Church.

But not to worry. There’s something pretty neat coming up.

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