The Wilderness

The board game "Outdoor Survival" (Avalon Hill, 1972) by Jim Dunnigan is listed, along with "Chainmail" in OD&D vol 1 Men & Magic, as necessary for playing Dungeons & Dragons.

The mapboard for Outdoor Survival (1972), representing 13,200 square miles of wilderness (3 miles/hex).

The game contains a three panel, 22" x 24" mapboard (depicted above), a cardboard set of die-cut Person Counters, Life Level Index cards, five Scenario cards, a "Rules of Play" booklet, a 24-page primer of outdoor survival techniques, and 1 six-sided die.

Dave Arneson used the map from Outdoor Survival in his "Blackmoor" campaign, prior to the publication of OD&D:

After the first year, the guys traveled around more and we began to use the Outdoor Survival Board (it was not until the third year that we actually moved into it). 

from "The First Fantasy Campaign" (1977)

In describing "Old Greyhawk Castle" in "How to Set Up Your Dungeons & Dragons Campaign (Part II of a Series), published in the fanzine Europa 6-8 (April, 1975), Gygax wrote:

The bottom level, number thirteen, contained an inescapable slide which took players 'clear through to China', from whence they had to return via 'Outdoor Adventure'.

from Europa 6-8 (Apr, 1975)

"The Wilderness" section in OD&D vol 3 The Underworld and Wilderness Adventures actually describes two types of wilderness adventure, the first using the "Outdoor Survival" board:

OUTDOOR SURVIVAL has a playing board perfect for general adventures.  Catch basins are castles, buildings are towns, and the balance of the terrain is as indicated.

from The Underworld & Wilderness Adventures, pg 15

Wayne Rossi took an in-depth look at the setting implications of the OD&D wilderness rules in a series of posts on his blog "Semper Initiativus Unum" in 2013.  These were later combined into a single document, entitled The Original D&D Setting.

Michael Mornard, a player in the original Greyhawk campaign (interviewed here), provided additional insights in this discussion thread, stating "One thing to make clear, though, is that we were in no way limited to the area of ONE Outdoor Survival map; you could keep going in any direction.  The OS map was simply the "generic terrain map" for any section of outdoors." and, more intriguingly, "Gary absolutely used the Outdoor Survival map for wilderness adventures.  Greyhawk was near the center of the left edge."

Rob Kuntz, co-DM in Greyhawk campaign, confirms Gary's use of the "Outdoor Survival" board, in this post on his blog "Lake Geneva Original RPG Campaign" in 2013.

The second type of wilderness adventure is the exploratory hex-crawl:

Exploratory journeys, such as expeditions to find land suitable for a castle or in search of some legendary treasure are handled in an entirely different manner.

from The Underworld & Wilderness Adventures, pg 15

Cover illustration for the Hexagonal Mapping Booklet (1980/1), by Bill Willingham

The DM is expected to create their own "referee's" map, unknown to the players, for the territory surrounding their dungeon:

When the players venture into this area, they should have a blank hexagon map, and as they move over each hex the referee will inform them as to what kind of terrain is in that hex.  This form of exploring will eventually enable the players to know the lay of the land in their immediate area and thus be able to select a site upon which to build their castles.

from The Underworld & Wilderness Adventures, pg 16

Arneson provides advice on "Drawing Your Own Map" in "The First Fantasy Campaign" (1977), using hex-by-hex random determination of terrain, with additional rules for human habitation and area pattern in hexes.

Gygax describes a more freestyle approach, in Europa 6-8:

Step 2 requires sitting down with a large piece of hex ruled paper and drawing a large scale map.  A map with a scale of 1 hex = 1 mile (or 2 kilometers for those of you who go in for recent faddish modes of measure) (yes, I often use rods, chains, furlongs, and leagues too!) will allow you to use your imagination to devise some interesting terrain and places, and it will be about right for your player operations such as exploring, camping, adventuring, and eventually building their strongholds.  Even such small things as a witch's hut and side entrances to the dungeon can be shown on the map.  The central features of the map must be the major town and the dungeon entrance.

from Europa 6-8 (Apr, 1975)

I'm not sure whether any of Gary's original maps of the territory around Greyhawk Castle exist.  Darlene's gorgeous maps from the "World of Greyhawk" folio (1980) were created specifically for that project, although differed from Gary's original maps.