The first poll you will want is to determine the basic genre of the shared world. You might be able to skip this poll if the group was formed around a single genre.
The basic genre's are:
After deciding the basic genre, you will need to look at the sub-genres. A number of the sub-genre's are repeated between genre's. Explanations of the sub-genre's, and how they can commonly be mixed is explained later in the page. The sub-genre's are explained in alphabetical order, not in the order of the major genre's.
Fantasy can include many things, some of which are cross overs from other genre's.
Historical usually means some sort of alternate history if you are talking designing a world for role playing. If you are going to do role playing in an actual historical context you really don't need to design a world. Instead of designing a world, you research the real world. The proto-typical alternate history is one where the South wins the War of Northern Aggression, aka American Civil War. Sub-genre's include:
Modern is more of time period, but does allow for other genre's within it's heading.
This covers a number of
This is a world that is Earth, but the characters or story takes place after some change in the history. The proto-typical alternate history is one where the Confederacy wins the American Civil War, and then writing stories that take place after that change has occured. The further from the initial event, the greater the changes will normally be. Classic examples of alternate history include: Harry Turtledove's So Few Remain and the 12 or so follow on books in the series. When building this type of world, you need to decide upon the initial change and then procede to determine those changes that arise out of the different outcome.
This is a different form of alternate history. The characters come from modern Earth and are transported to a world that has an alternate history. The year hasn't changed, but history was changed, and the characters moved from our world to the alternate history world. Classic examples of cross time include H. Beam Piper's Lord Kalven of Otherwheni and it's follow on by Roland Green Great Kings War (availiable as a free legal down load from the Baen Free Libary. Other examples are Harry Turtledove's Gunpowder Empire and Curious Notions (the Cross Time series); S.M. Stirling's Conquestador and the TV show Sliders.
This sub-genre needs work. I see a big difference between the worlds in D&D and Tolkien's Middle Earth.
Historical fantasy is similar to alternate history. The world is a historical version of Earth with fantasy / magic added. Examples include: Stasheff's Wizard In Rhyme series
Urban fantasy is a relatively new sub-genre of fantasy literature. The time and place is our modern, or near modern Earth. Added to our modern society are fantasy elements such as Elves, Dwarves and hidden magicians. The key is fantasy elements that are Examples of books include Harry Potter, Mercedes Lackey's Chrome Borne series (Born To Run, Chrome Circle) and her Diane Tregard series. From television it would include Buffy The Vampire Slayer, Charmed, and Sabrina: The Teenaged Witch. Movies would include The Craft, Practical Magic, The Witches of Eastwick and similar.
Neverwhere, Sandman, American Gods by Neil Gaiman Mage - both the comic book and the White Wolf roleplaying game (as all World of Darkness could be regarded, especially Changeling) Long Dark Teatime of the Soul by Douglas Adams The Anita Blake series Laurell K Hamilton (in fact, any series with hidden or semi-hidden magical beings) Harry Potter