I was looking at the 40-pin pinout and I couldn't help noticing that there doesn't seem to be a logical order to the placement of the GPIO pins. Even allowing that there may be a technical reason for them to not all be grouped together, if you follow the physical pin order and ignore non-GPIO pins, the GPIO pins appear in this order:
2 3 4 14 15 17 18 27 22 23 24 10 9 25 11 8 7 5 6 12 13 19 16 26 20 21
I'm curious if there's some technical or logical reason that the pins are numbered in such a way. I would have expected that the GPIO pins number could be adjusted logically within the RPi so that they could have an intuitive order (for example, why not just swap the names of GPIO14 and GPIO5?), so I'm guessing there's a good rationale that I simply don't understand.