Any theories to why Zombies seem to be an American / European / somewhat Japanese / Australian phenomenon? Perhaps a cultural byproduct of modernity?
From the Oxford Internet Institute, whose description of the data vizualization's construction offers a much more mundane answer:
In order to measure the amount of content about zombies indexed by Google, a dataset was created based on a 0.25 x 0.25 degree grid of all the land mass in the world (roughly 250,000 points). A buffer was then constructed for each point using a sliding variable size based on the great circle distance to neighbouring points in the grid pattern. It was important to adjust this value in order to compensate for decreasing distance between longitudes as the software moves from the equator to the poles. For each point and buffer combination a search was run in Google Maps to measure the total number of hits for user-generated content at each location (as defined by Google).