Official urxvt Perl extension reference

“The area of each icon is proportional to the sum of the reach of all sites using that icon. When both a bare domain name and its “www.” counterpart used the same icon, only one of them was counted. The smallest icons–those corresponding to sites with approximately 0.0001% reach–are scaled to 16x16 pixels. The largest icon (Google) is 11,936 x 11,936 pixels, and the whole diagram is 37,440 x 37,440.”