On Commons Categories should be disambiguated like Wikipedia articles but should there should be a higher threshold for primary topics, generally if WP wants 75% in this specific case, we want 90% the others combined or if the topic is overwhelmingly more important than others with that term. If at least 90% of people who search for "London" want the capital for example the category should be called "London" not "London, England" for example (with the dab page at Category:London (disambiguation). However when this isn't the case as with the categories for Mercury or Perth then they should be disambiguated because they fall below this. Categories however should not be preemptively disambiguated unless a specific guideline states otherwise (like USPLACE) or because of a good reason and shouldn't be disambiguated simply because of part title matches unless there is likely confusion in a general context. For example we reasonably expect to see Abraham Lincoln at Lincoln (disambiguation), but very few sources would refer to the waltz composer Harry J. Lincoln by an unqualified "Lincoln", so he would only be included in the Lincoln (surname) category and not listed at Category:Lincoln as well. There is no single criterion for defining a primary topic. However, there are two major aspects that are commonly discussed in connection with primary topics:
- A topic is primary for a term, with respect to usage if it is the topic sought when a reader searches for that term at least 90% of the time.
- A topic is primary for a term, with respect to long-term significance, if it has substantially greater enduring notability and educational value than all of the other topic associated with that term combined.
Keep in mind that a topic may have more than one category associated with it such as the city Cambridge also having the university or Wells covering broadly all types of wells. If there is a primary general meaning that should be at the base name.
Note this briefly explains disambiguation for categories on Commons, to avoid duplicating much content, please refer to Wikipedia's disambiguation guidelines.