Nexstar Media Group and Sinclair Broadcast Group’s decision highlights the influence and sometimes-tenuous relationship local TV station owners have with national broadcasters such as Disney-owned ABC. Here are key facts about the two companies, which collectively own about a quarter of ABC affiliates, including in some bigger cities like Washington, D.C.Nexstar Media GroupNexstar Media Group, based in Irving, Texas, operates 28 ABC affiliates. Last month, it announced a $6.2 billion deal to buy TEGNA Inc., which owns 64 other TV stations. Sinclair Broadcast GroupSinclair Broadcast Group, based in Hunt Valley, Maryland, operates 38 local ABC affiliates. Its ABC affiliates include stations in Washington, D.C., Portland, Ore., Chattanooga, Tennessee, and other cities.