Surprisingly, nobody really knows. In the First Fantasy Campaign Arneson described drawing his first Blackmoor map:
"The basic campaign area reproduced on a large mapsheet outside this book, was originally drawn from some olden Dutch maps. Much of the rationale and scale was based on data found with the Dutch maps."
We have copies of that original map - its the one we have discussed that was enclosed with a letter to Rob Kuntz in March of 1971. However when we look to that original map, no scale is given, nor is there a scale on the next map we have from Arneson, the "Sketch map" reproduced as an illustration in the FFC.
We can get a rough idea - a very rough idea - if we take Arneson at his word and plop his March 1971 map onto a map of the Netherlands as shown below:
Of course there are a lot of assumptions here. The map of the Netherlands I used is probably not the one Arneson used. I just picked an older but modernish map with clear borders to serve the purpose. Further I placed the Blackmoor Map/Northern Marches map in what seems to be the likely location based on a few coastlines. In any case, the Blackmoor map stretches pretty much across the width of Holland and those coastline features do fit quite well.
Alright then, using the scale of the Netherlands map, from side to side the Northern Marches map is somewhere in the ball park of 120 kilometers, or about 75 miles.
Possibly Arneson was focused on a smaller area and the distance should be less, but it is hard to see where that could be in terms of analogous features in the Netherlands. Possibly he meant the map to be bigger, although if we stay inside the borders of the Netherlands there's not a lot more room, perhaps another 25 miles at most, and that would mean moving the Blackmoor map to an area where there are no matching features, so we can be reasonably sure the 75 miles end to end scale, give or take a few miles, is about right for the original Blackmoor/Northern Marches map.
Of course, that scale is not at all what we find with later maps. Instead, as we will see, scales are all over the place.
The first Blackmoor regional maps to be published came with Judges Guild's First Fantasy Campaign, and were drawn by Bob Bledsaw. These maps do have a scale, and they also encompass a much larger area of the Northern Marches than what we see in Arneson's original map. Indeed, as we will see, maps of Blackmoor have sometimes taken in less, sometimes more, of the surrounding area.
On the JG maps themselves, the scale is given as 10 miles per hex, and on the same page as the "sketch map" of Blackmoor, Arneson writes:
"In redrawing the first campaign map, I have decided that it would be advantageous to make some minor changes along the south and west borders to link it with the Judges Guild's "Known World" area (as shown in the Guide to the City State). My map is twice the scale, 10 miles per hex, and fits into the northeastern corner, bordering the Valley of the Ancients."
Ten miles per "square" was a favorite scale Arenson used in a number of instances, so ten miles per hex here isn't surprising. What is a bit more confusing however is the "twice the scale." statement - twice the scale of what? Neither of Arneson's earlier maps have any scale on them. Possibly he is merely referring here to the fact that D&D used 5 mile hexes and that was a change Gygax had made late during the D&D draft process. (Edit: see comments below for the explanation)
In any case, I'm not convinced that the Judges Guild maps give us a "true" scale, whatever the hex size. Possibly they do, but just as possibly it was Bledsaw who determined the physical size of the hexes he overlaid on the map. Arneson notoriously deferred on details, allowing others to set things up however they wanted. Arneson clearly told Bledsaw to make the hexes ten miles across, but probably did not give much direction on the actual physical size a hex should be on the map. In other words, I think it likely Bledsaw laid a hex grid on top of the map as he pleased and called the hexes 10 miles across.
Whatever merits or faults they had, these maps from Judges Guild are the first scaled maps of the area.
The next publication that to have a map of the whole of Blackmoor is DA1. The DA1 map has the hexes marked now as 24 miles across, even though the hexes appear to be physically about the same size they were on the JG map. Twenty-four miles is in keeping with the new 6 mile hex system introduced by Steve Marsh in the Expert set rules and carried through to all the later Basic D&D sets.
So Blackmoor appears to have grown - a lot - more than double in fact. Interestingly however, when a new map was created for DA4, the scale was changed again, but reduced by half, so that the DA4 map was now down to 12 miles per hex, and this scale was apparently retconned to new printings of the earlier modules.
If this isn't confusing enough, new maps at new scales appear during the d20 Zeitgiest games era. The principal map was released as a fold out with the Campaign Sourcebook and had hexes slightly larger than the previous Judges Guild and TSR iterations. These were given as 12.5 miles per hex. The accompanying scale bar has 25 miles per inch.
ZG also produced a hand drawn, hexless map by Clayton Bunce.
Here it gets interesting because two different scales - again - are given for this map at different releases. Though both versions are identical and use the same scale bar, one iteration of the Bunch map has the bar marked 0-80 in 20 mile blocks with the other is 0-40 in 10 mile blocks.
Thus the era of "official" Blackmoor publications ended with as much scale confusion as it started.
Now, given that these various maps cover differing amounts of territory, perhaps the best way to grasp these differences in scale, is to consider two points on the map. In the table below I compare the differences in distance between the towns of Blackmoor and Jackport, These two locations were chosen because they are on most of the maps and have a fairly straight, close-to-horizontal road between them.
We can use the scale bars on the ZG maps to give us a pretty good sense of the distance between our reference points, like so:
Roughly speaking, looking at the various maps and scales yields these figures for the distance between Jackport and the town of Blackmoor:
Map |
# of Hexes Between |
Jackport
to Blackmoor Town in Miles |
March
1971 Map at 75 miles E-W |
n/a |
27 |
Bledsaw
1977 Maps |
12.5 |
125 |
TSR
24 mile hex |
12 |
288 |
TSR
12 mile hex |
12 |
144 |
ZG
12.5 mile hex |
9 |
112 |
ZG
Bunce map 0-40 scale |
n/a |
37 |
ZG
Bunce map 0-80 scale |
n/a |
74 |
Greyhawk
Dungeon mag |
.8 |
25 |
Note that I included a Greyhawk map estimate for fun. Jackport isn't on the Greyhawk maps but we can plot it useing Mosshold/Maus and it comes out to a scale comparable to the 1970 map estimated scale.
Whats' interesting to note is that either version of the Bunce map, but especially the smaller scale is closer to the scale we got above for the original March 1970 map, and the Greyhawk map came out virtually the same.
The other scales measure the distance in hundreds of miles and make for a rather large Blackmoor, and this would seem to be at odds with Arneson's own characterization of Blackmoor in an interview published in Pegasus 14 in 1999. He said, "There are certainly worlds out there with far more depth and creativity in them than Blackmoor had or has. It was just my little fantasy campaign, in an area not much bigger than a couple of large states put together, maybe Montana."
We can compare the various scales given to real world US states. Conveniently, the distance between Philadelphia and Pittsburgh is quite close to the largest scale of 24 miles per hex. When the Blackmoor 24 mile per hex map is superimposed on the Eastern United States with Philadelphia and Pittsburgh as reference points, here is what you get:
At that scale, Blackmoor is literally half a continent.
Downsizing to the 125 mile distance between Jackport and Blackmoor town (roughly Philadelphia to Gettysburgh) leaves us with a Blackmoor about this big:
In this case Blackmoor covers the size of five or six American states. Depending on how you view Blackmoor, that could be just right, but if your idea of Blackmoor is an isolated northern land akin to Ireland or Estonia or Montana, you may find this still to be overly large. As an interesting comparison, here is a similar map of with four European countries in roughly the same location:
At the scale of ten miles per hex used on the Judges Guild map, Blackmoor is about equivalent to three Great Britains, side by side.
On the other end of the spectrum, matching the real world with our scale of 27 miles between Jackport and Blackmoor town results in this:
Even at this smaller scale, Blackmoor is still quite a large area - larger than the state of New Jersey with plenty of room for adventure at perhaps a bit more manageable size. For me, this is just about right. It is also convenient that Greyhawks' Blackmoor appears to be at about the same scale.
Ultimately however there is no definitive answer to the question of scale for Blackmoor, and game masters can choose from the various scales for what works best for their campaign.