Which aspect of advertising involves physical locations like airports and buses?

Transit advertising is the correct answer because it specifically refers to ads placed on or in transportation modes such as buses, subways, taxis, and at transit stations, including airports. This type of advertising takes advantage of the high foot traffic and visibility that these locations offer, allowing brands to reach a diverse audience in practical settings.

In contrast, digital advertising focuses on online platforms like social media, search engines, or websites, while print advertising pertains to physical printed media like newspapers and magazines. Outdoor advertising includes billboards and other large-scale visual campaigns not limited to transit vehicles or locations.