The listing of those fifty terrain types-- with no fewer than ten different types of "plains" and includes representative art for all of them-- comes from a 1931 article by Erwin Raisz (of whom I had never heard before), who sets out a system to standardize the illustration of terrain according to the geographic type of the area, but with incorporating the peculiar idiosyncracies of the land itself. Raisz is quoted as saying:
For the study of settlement, land utilization, or any other aspect of man’s occupation of the earth it is more important to have information about the ruggedness, trend, and character of mountains, ridges, plains, plateaus,
canyons, and so on-in a word, the physiography of the region.
And I can say that such would be eminently important to the more mundane aspects of both role-playing and wargaming. On the whole, it's very evocative of Renaissance-era maps, to my eye. It is most definitely the antithesis of modern cartography, which is very modern and scientific, with elevation lines and so forth. Much as I can see the appeal of such a modernist approach to mapping, I vastly prefer the evocative nature of this sort of cartography for gaming purposes.
The old Wilderlands maps are something of an adaptation of this sort of map-making; taking these sorts of naturalistic terrain markers (in a simplified form; mountains are mountains) and applying a hex map overlay. The famed Greyhawk poster maps by Darlene are more of an abstraction of that principle; the terrain types, to a large extent, are made to conform to the hex grid (although she does do so in a very aesthetically pleasing way, as well as the way she works the necessary text of the map in with the features they describe). At the other end of the scale, of course, are more traditional wargaming maps (of the AH or SPI school), where the terrain is laid out at the hex level in an almost-abstract fashion.
Krygier also makes the point that this sort of cartography is largely impossible with today's modern digital cartography. I'm not convinced that something reasonable couldn't be done in the Raiszian style, but I hardly claim to be an expert in digital cartography.
All in all, I find myself now inspired to do a whole lot of mapping for my campaign.