Complex sentence: Runnels County is the adjacent county to San Angelo, but the majority of the residents in the county watch local television stations that broadcast from Abilene, so the county is assigned to the Abilene-Sweetwater television market by Nielsen.
Split into simpler sentences: Runnels County is the adjacent county to San Angelo but the majority of the residents in the county watch local television stations that broadcast out of Abilene. This is why the county is assigned to the Abilene-Sweetwater television market by Nielsen.