Category:Earth is a 'root' category for categories about wikis where the wiki is associated with a place on our planet. If a wikis issues aren't really related to any particular location on Earth, then it should be in this very category. If a wiki is related to some specialized place on Earth then you should try to find the most specialized subcategory you can that matches the wiki's 'scope'. The subcategories can work down to for more and more specific places on Earth all the way down to neighborhoods or particular buildings (where for example, a business might be located) if the neighborhoods or buildings actually have lots of wikis whose geographic scope is specifically that neighborhood or building.
See the talk page for this category for more on the details of how this works if you're interested in getting involved with the place categories.
This category has the following 19 subcategories, out of 19 total.
Pages in category “Earth”
The following 70 pages are in this category, out of 70 total.