Final answer:
The organization responsible for local audience measurement for television is Nielsen Station Index. Nielsen ratings guide television stations on show popularity and advertising rates. A local station broadcasting national network programming is called an affiliate.
Step-by-step explanation:
Nielsen, along with its subsidiary Harris Interactive, has been pivotal in measuring television and media viewership. Nielsen ratings are crucial as they assist television stations in determining which shows attract enough viewers to remain on air and help set advertising rates based on the audience size. This survey data also informs future trends in political and market arenas.
To address the additional question, a local station that broadcasts national network programming is known as an affiliate. This term references local television channels that partner with major networks to air their programming to a regional audience.