Luxury resources tend to clump, which provides for good spots for wealthy cities, and promotes their trade. Luxuries can be allowed to clump, since their particular presence or absence won't break the game. The only provide commerce, so you just get a "wealthy" city nearby and not a "phenominally productive" one. I have also noticed that natural-silver seems only to occur on tundra-hills, gold on desert/plains hills, and gems in
Strategic resources are almost always spread apart somewhat evenly. This is becuase you generally only need 1 of any given type, and their presence or absence has major effects on the outcome of the game.
Food resources are also spread apart, 'cause having like 5 of them together at once would create a heinously prolific city. These do tend to clump more than strategic resources, but that's probably due more to continental distrubutions (like corn only on 1 continent) and just a higher volume than strategics.
) against the whole world with only construction (not as expensive as maceman's path).
