The reason is probably because the map is only showing the top 10 for each list of countries. Vietnam is probably not in the top ten for arrivals in Poland.
No, you need to have units on your data. Without units, numbers mean nothing. You select a country, and then you're presented with a list of other countries and some numbers. It's not clear that these are lifetime immigrants or permanent residents. There should be a title on the country info box "Total lifetime immigrants" or "Total lifetime emigrants", and ideally a legend at the bottom defining what that means.
It's also confusing in that the number format follows a European convention of using decimal points rather than commas in between every three digits the numbers, though I can accept that localising your site isn't a big concern.
It also works in IE. I just showed it on ie8. It's less fluid, and you loose some functionality, but the main ones are still working. Kudos to Raphael.js
I totally agree, that is the main missing feature in my opinion and the reason why I added a select box on top.
At first I wanted to use polymaps, which supports zoom and pan, but I found it difficult to draw on top of it (for the "arrows") and it lacked ie support. So I went for Raphael.js, but found it to cumbersome to implement zoom and pan.
I have tried to add arrows at some point, but it cluttered the visualization too much (especially for countries where migrations are quite local : limited to border-sharing countries).
That said, there may be a solution I did not think about.
You could over impose three dotted lines with a different color/dot-spacing to each connecting line, then set a timeout and alternate their visibility accordingly, so you can get a "dots flowing inside the line" effect. Not sure if this can work with canvas though.
How about drawing the arrowhead on the middle of the line? (And not drawing it on short lines. The arrowheads on the long lines will reveal whether 'departures' or 'arrivals' are depicted)
The site is currently javascript only, the server is only serving static files, and the svg tags are generated in the browser using Raphael.js.
That said, I have already been pondering about this for a previous projects: http://populationpyramid.net and there are solutions : either export the svg tags through an ajax query to a server that would then render it as PNG, or create a script that would create the svg files directly from the data. I did not take time to implement this, though (I have to sleep sometimes...)
