Geofiction
Geofiction is a hobby where people design imaginary cities, countries or entire worlds, including placenames, culture, social and political structures and even constructed languages (conlangs), primarily for personal enjoyment.
It may by contrasted with the creation of constructed worlds, which are typically used to enhance the realisation of a fictional universe for a story or collection of stories, whereas geofiction is "world creation" for its own sake, sometimes but not always for creating a story setting, but always for fun.
Geofiction may encompass diagrams of imaginary streets drawn by a young child to elaborate, internally self-consistent worlds created as a hobby or life-long project by adults. Alternately, geofiction is fiction where the (created) setting is the focus.
A good example of the art of geofiction is manifested in The Lord of the Rings, where J. R. R. Tolkien devised an entire fictional world (Middle-earth) populated by various species and races (man, elf, hobbit, etc), along with imaginary languages and alphabets for his creations, all initially for his own amusement.
Micronations are sometimes considered an elaborate form of geofiction.
[Eshraval: A Nation of Your Own] is a new and more developed game of geofiction, incorporating a nation and business simulation to allow players the opportunity to run their own nation and businesses on a realistic and consistent game world.
ImagiNations, a network of geofictional planets and the brainchild of author Edward Mooney, Jr., is a prime example of highly developed geofiction as a hobby. Vexillium is the oldest and primary geofictional planet of the ImagiNations network.