What's the difference?
A Designated Market Area (DMA) is a geographic area of the US that represents specific television markets defined by, and annually updated by, Nielsen Media Research. There are currently 210 DMA markets in the U.S.
A Metropolitan Statistical Area (MSA) is a geographical area defined by the federal Office of Management and Budget (OMB) that represents the metropolitan area of a city. As of June 6, 2003, the OMB has defined a total of 362 Metropolitan Statistical Areas.
DMA is the most common, and often preferred means of Geo targeting an ad campaign. In the realm of digital advertising, Google DoubleClick, arguably the largest ad serving platform, allows users to Geo target ads via Country, Region, City, Zip Code or "US Metro Areas", which is in fact DMA targeting. In order to achieve accurate MSA targeting for digital ad-serving it is recommended that one converts the desired MSA markets into a relevant City or Zip Code list.