One of the age old questions is "What is the perfect size for a wilderness hex?" It's right up there with "Pointy-top hex or flat-top hex?" (Aside, I have done several polls on this and a clear majority prefer flat-topped.) Gygax expresses a preferred scale here of 5 miles as "the greatest distance across a hex." That being said, in 1975 he published an article suggesting a 1-mile hex, so the above comment might have been specific to the Outdoor Survival board (see previous post).
Gygax includes encounter tables in this volume for desert/arid plants. Among the entries are Red/Black/Yellow/White Martians, Tharks, Apts, Banths, Thoats, Calots, White Apes, Orluks, Sith, Darseen. In other words, Edgar Rice Burroughs' Barsoom setting. ERB's Mars series is, arguably, the most referenced work in D&D. Even more than Tolkien (despite naming hobbits, balrogs, and such). Gygax knew what he was doing. Under Other Worlds, he says "Mars is given in these rules, but some other fantastic world or setting could be equally possible" (24).
Gygax leans on Chainmail for resolving mass combat and prefers miniatures on a field of 4' x 4' minimum and ideally 6' x 6' (25). But he notes that one could use paper counters and a hexagon or staggered-square board. He also covers command and control, naval battles, etc. All in frustratingly erratic detail, to be sure, but enough to perhaps get people going. [Edit: At Gary Con XIV, I got the privilege of playing a draft of Arneson's air-battle rules for D&D that never made it into Gary's version. The game was run by Griff, the director/creator of Secrets of Blackmoor.]
This is one of the most important paragraphs in original D&D, to my thinking.
"There are unquestionably areas which have been glossed over. While we deeply regret the necessity, space requires that we put in the essentials only, and the trimming will often have to be added by the referee and his players. We have attempted to furnish an ample framework, and building should be both easy and fun. In this light, we urge you to refrain from writing for rule interpretations or the like unless you are absolutely at a loss, for everything herein is fantastic, and the best way is to decide how you would like it to be, and then make it just that way! On the other hand, we are not loath to answer your questions, but why have us do any more of your imagining for you? Write to us and tell about your additions, ideas, and what have you. We could always do with a bit of improvement in our refereeing" (36).
This is pretty clearly a different Gygax than we see in the AD&D era. After a few years of answering rules questions and commenting (disparagingly) on others' interpretations, he tried to tighten down and codify D&D in a way that some feel killed the spirit of openness in the game.