|Middle Earth vs Newhon|
The post on white space the other day highlighted some differences between bottom-up and top-down setting design, and how bottom-up allows room for more dramatic changes as you go along; by starting small and developing the micro-setting, the DM can plug in emergent ideas without violating the big-picture aesthetic, because there is no big picture aesthetic. Bottom up is a way to mitigate the gamer ADD.
Anyway, I struck on a different metaphor - top-down is like an impressionist painting, and bottom-up is a mosaic. The picture caption refers to the different setting approaches taking by Professor Tolkien for Middle Earth in The Lord of the Rings, and Fritz Leiber's approach to Newhon in the stories of Fafhrd and the Gray Mouser.
Folks that sketch out the world, provide the history, and define an aesthetic that unifies the setting are painters - they cover the available canvass when creating that overarching picture. It looks great when you squint or view it from a distance, but when you get close you realize it's just broad brush strokes without a lot of detail.
The bottom-up approach is like building a mosaic out of tiles. Each tile is highly detailed and colorful, and you can zoom in real close to see the details. One tile doesn't define the color, size or style of the next. A similar metaphor for creation could be a quilt; everyone has seen those quilts with highly detailed squares, each with a unique pattern; the pattern on one square exerts no influence on the next square over, and the end result might be fairly discordant, but it was fun to put together along the way.
Many of the high concept worlds that TSR and WOTC created are clearly top-down, and it's not hard to think of something an old school gamer might want to put in one of those worlds that would be fairly discordant. The one TSR setting I can think of that's clearly a bottom-up mosaic is Mystara - the Known World from BX and then the BECMI era. Each new Gazetteer extended the setting in a modular and unusual new way; I could probably write an "ode to gonzo" just based on the Mystara sprawl. It's the ultimate D&D kitchen sink setting.