A media market, broadcast market, media region, designated market area (DMA), television market area, or simply market is a region where the population can receive the same (or similar) television and radio station offerings, and may also include other types of media including newspapers and Internet content. They can coincide or overlap with one or more metropolitan areas, though rural regions with few significant population centers can also be designated as markets. Conversely, very large metropolitan areas can sometimes be subdivided into multiple segments. Market regions may overlap, meaning that people residing on the edge of one media market may be able to receive content from other nearby markets. They are widely used in audience measurements, which are compiled in the United States by Nielsen Media Research. Nielsen measures both television and radio audiences since its acquisition of Arbitron, which was completed in September 2013.[1]

Markets are identified by the largest city, which is usually located in the center of the market region. However, geography and the fact that some metropolitan areas have large cities separated by some distance can make markets have unusual shapes and result in two, three, or more names being used to identify a single region (such as Wichita-Hutchinson, Kansas; Chico-Redding, California; Albany-Schenectady-Troy, New York; and Harrisburg-Lebanon-Lancaster-York, Pennsylvania).

In the United States, radio markets are generally a bit smaller than their television counterparts, as broadcast power restrictions are stricter for radio than TV, and TV reaches further via cable. AM band and FM band radio ratings are sometimes separated, as are broadcast and cable television. Market researchers also subdivide ratings demographically between different age groups, genders, and ethnic backgrounds; as well as psychographically between income levels and other non-physical factors. This information is used by advertisers to determine how to reach a specific audience. In countries such as the United Kingdom [citation needed], a government body defines the media markets; in countries such as the United States, media regions are defined by a privately held institution, without government status.

https://en.wikipedia.org/wiki/List_of_television_stations_in_North_America_by_media_market

According to Nielsen’s 2018-2019 rankings, there are presently 210 Designated Market Areas (“DMAs”) in the United States, as follows…