Gygax and Arneson suggest using the map from Outdoor Survival as a default wilderness map for GMs starting a campaign. The suggestion is to start with just local maps of a starting town, outside of a dungeon, and actual dungeon levels, then fill in details of the rest of the world as you play, using the Outdoor Survival map as a terrain guide, stocking or describing castles and towns on the map as they are encountered. On the OD&D 74 forumes, there's a discussion about other maps you could use in the same way, like the one from Barbarian Prince. I suggested Magic Realm could be an option, since the individual cardboard hexes mean each GM can have a unique wilderness map.
That got me thinking: what if you had a set of tiles -- wilderness geomorphs -- with well-drawn terrain and generic labels like "town", "keep", "cave" or "ruins" on them, plus a few blank wilderness geomorphs to customize, so that you could create your setting piece-by-piece, laying out tiles for the players as they explore so that they can get an idea of what they can see, while you would take notes of which tiles you placed and what the generic elements contain? You could start out just placing a 3x3 arrangement of tiles, with the starting location in the center, and offer basic notes of general terrain in each direction beyond that. The players decide whether to explore locally or head towards one of the surrounding tiles, or beyond.
Hex tiles like those in Magic Realm seem like a lot of work, so maybe it would be easier to use simple square tiles with a staggered square grid, which provides features similar to a hex grid.