Location can mean many different things:
- Specific range of pages (for articles, book chapters, etc.)
- URL for a website
- DOI (digital object identifier) for an article
- Location of a physical object (work of art in a museum)
For books, city of publication is not required, unless it is relevant. For example, if you are citing the British edition of a text, including London as the city of publication would be useful.
For more information on locations, see pages 46-50 in the MLA Handbook.