The 8-mile hex
MorfieThe 24 mile hex is based on the average human travel per day in BECMI, dependent on terrain of course. In AD&D's Greyhawk 30 miles per day was the average travel (Based on 10 hours @ 3mph, instead of 8 hrs) so the Darlene map has 30 mile hexes.
8 is divisible by most of the Traveling Rates by Terrain Table, but then so is 6. Expert Set's map of Karameikos and X1's Isle of Dread were at 6 mile hexes.
But when converting a 24 mile hex to break it down into more detail, 8 fits in a lot better with a 3 x 3 format in 3 directions of travel. Hence the GAZ maps are 8 mile hexes. Conversely when scaling up a 24 mile hex, 72 miles fits in and that was used for other maps. Some fan maps attempt to break down 8 miles further into 2 2/3 mile hexes.