World Population Density ~ People per Square Km

Lovely hi-res worldmap of people per square kilometer by daysleeperrr posted on Reddit MapPorn. The comments are also illustrative. And author's note...

"Took about four hours, with notepad to write the map generator script and photoshop for the legend. I downloaded an .asc (ascii) file [with pop density, about] 30 million records. Converted the huge 200 MB file to a smaller file with this php script in which 30 catogories were used instead of exact numbers. [...] Convert the file to an image. For that I used the PHP GD Library [and script. And finally] Added the legend and some color using photoshop. It's the first time I tried creating a map using programming language only, instead of ArcGIS or tools like that. I was surprised how little lines of code were needed in order to generate such a map. If someone has suggestions for improvement let me know ;-)"