When creating a new wiki, you may want to consider whether a wiki on that topic already exists. For example, if you want to create a wiki to document information about Star Wars, ask yourself if your wiki will be offering something that Wookieepedia does not. If your wiki idea does not offer something new, we’d suggest that you not create a duplicate wiki but instead that you offer your expertise on the wiki communities that already exist.
Find a niche topic
Let’s stick with the example of a Star Wars wiki. Creating a wiki that is meant to serve as a comprehensive resource will likely not yield you any results. Wookieepedia has a years-long head start and already documents most information from the Star Wars franchise. Because of that, if you want to create a Star Wars wiki, you should find a specific topic within the Star Wars universe to create a wiki about instead of just an all-purpose Star Wars wiki.
With that said, you want to figure out if you can create and nourish a sub-topic of the overall topic. Competing with or overtaking a wiki that has been established for years is highly unlikely, but further developing a sub-topic in its own wiki is certainly possible. Besides, one of the core philosophies of wiki building is collaboration, not competition. You should find a way to co-exist, and a niche topic can do just that.
Create and promote uniqueness
So, you’ve created a niche wiki. Let’s say your wiki is called the Jedi Wiki, and your goal is to provide lots of great info about Jedi—Jedi characters, Jedi organizations, overviews and analysis of Jedi philosophies, etc. There are lots of things you can do with a niche topic like that, but you need to promote the fact that your topic is offering something that the main wiki does not. To do that, you need to offer something unique.
If the end result of your effort to create a niche wiki is to cover the exact same information as the main wiki, then your wiki has proven to be an unnecessary duplicate. You want to offer something that the main wiki does not. For example, Wookieepedia covers in-universe information (biographies of characters, timelines of events, and so forth), but the Star Wars: The Old Republic Wiki covers gameplay information for the video game. That allows The Old Republic Wiki to be a resource for gamers in a way that Wookieepedia does not, and it is what makes The Old Republic Wiki successful. That is the type of niche topic you want to find and cultivate.
Now that you’ve found that niche topic, you want to promote that. Make your main page say things that are clear in how your wiki differs from the main one. You don’t need to actually list differences in comparison, but there could be key buzzwords that provide a reader with the means to understand that difference. For example, a video game wiki like The Old Republic Wiki could say something akin to “a comprehensive resource for gamers,” which shows that it would specifically target a gamer as opposed to someone looking for historical information on Star Wars lore.
In the same way that you can attract contributors to your site, consider how your wiki is promoted in general. If you have a Facebook or Twitter page, for example, promote it in a way that showcases its uniqueness. If you are promoting a wiki like The Old Republic, promote it in a way that targets gamers. That way, your core audience can know what your topic is and gravitate to it.
Start a friendship with the main wiki
One of the best ways to help promote your topic is to be on good and friendly terms with the main wiki. Take the Star Wars wikis as an example. Wookieepedia lists the LEGO®Star Wars Wiki, the Star Wars: The Old Republic Wiki, and other Star Wars wikis and websites as their official friends. That gives those wikis a noticeable place on Wookieepedia’s main page, and it acknowledges the fact that these wikis share an overall topic but are offering their readers and contributors different things. Wookieepedia has chosen to be a wiki that documents the in-universe lore of the franchise, so they can direct gamers and gameplay enthusiasts to the Star Wars: The Old Republic Wiki. That makes that friendship a sort of partnership that benefits them both and respects both topics.
Even if there is no official friend process like there is with Wookieepedia, having a relationship and an acknowledged and respected difference in the focus of the topic is a good thing. It allows both wikis to co-exist under the umbrella of one topic while respectfully working towards shared yet slightly different goals.
Of course, that friendship may not always happen. There may be a main wiki that wants to be everything and own everything about a topic, and they may not like the fact that another wiki is competing with that. For your part, don’t worry about that. Even if your wiki is a duplicate, there’s nothing inherently wrong with that. We do allow them, after all.
Should you find yourself in a dispute, the best thing to do is to ignore it unless it becomes a disruption on your wiki, in which case you have administrative tools to help with that. You can also contact Wikia for help and advice in that regard. Remember that you are free to create a wiki with a similar topic to one that already exists, just try to make it somewhat different as advised earlier in the page.
Now, the following advice is for those who are disputing the new wiki’s existence: unless the new wiki is directly copying content from your wiki without attributing it under the terms of the Creative Commons copyright license, there is no need for you to make an issue out of its existence. If you find yourself annoyed or upset that it was created, the best thing to do is let it go. You are already on an established and successful wiki, so you really have nothing to worry about.
Instead of debating the issue, try to become friends as outlined earlier. It really is the best thing for everyone!