When it comes to emphasizing the boundaries of a particular area, we often use the phrase "mark the periphery." However, there are a number of synonyms that can be used in its place, such as "define the outskirts," "highlight the border," "outline the edges," "delineate the limits," and "demarcate the boundary." These phrases can be particularly useful when describing a geographical location or the limits of a social or cultural group. Choosing the right synonym can help to provide clarity and precision in communication, allowing us to more effectively convey the nuances of meaning we wish to express.