Eastern had a hub at ATL, and competed on a number of city pairs with DL. This was in addition to numerous point to point routs. National was primarly Atlantic seaboard to Florida and Fla along the Gulf coast. They might have had a micro hub at MSY and /or JAX.
UA was then the largest domestic airline with iots hubs at ORD and DEN. Also a mini hub at CLE with routs to the east coast and numerous great lakes/mid west cities, ie: FWA, SBN, GRR,LAN, etc. Most were 737-200's with an occasional 727, either 100 or 200. The CLE hub had fligts to MIA/TPA/FLL & ATL. AA was focused at ORD and DFW as now, but also had several point to points in the east, ie: LGA-DTW,LGA-BNA?,etc. TWA had a micro hub at PIT for a while with flights to IND,CMH,CVG and DAY among others as well as STL & MCI. Deltas routes followed the old Delta pattern of the South east and the C&S routs acquired in the 50's from the midwest to ATL & Florida. Hope this helps.