Didn't notice the tool jumping around till you pointed it out; now I can't stop seeing it. Pushing against left and bottom would definitely be better, especially since there isn't much to see there.
Embarrassingly, I'm not sure what the projection is. The data is described as 'estimates of human population for the years 1990, 1995, and 2000 by 30 arc-second (1km) grid cells'. I did some aggregation to reduce the file size and then just converted that grid to pixel values stretched across the screen:
y = d3.scale.linear()
.domain([0, longitudes.length])
.range([0, height]),