Commons:Guide to layout/Gallery pages
Galleries are a complement to categories, as another way of displaying media. Galleries are useful as showcasing the best, most illustrative, informative and interesting images of a category. They allow files to be annotated with captions, shown at better sizes than the category default, organised in tables, etc. They are also useful for presenting material in a logical order, something categories have a limited ability to do. For example, compare Tennis to Category:Tennis. Information on gallery pages can be presented in a hierarchical manner, such as Pronunciation of Dutch municipality names and United States.
Galleries typically begin with short captions that briefly introduce the topic in many languages (these can be automatically generated using Commons Sum-it-up), followed by headed sections that typically use the <gallery> tag (see meta page for guidance). The files should be followed by interwiki links (also generated by Sum-it-up) and at least one category. Gallery pages must be in at least one category.
A good way to design a new gallery page is to adapt an existing one from a similar topic. Species (plants/animals) pages will necessarily be different to location (cities/countries) pages.
A special series of gallery pages are the Atlas pages, that can be found at Atlas.