This map looks more reasonable and less gerrymandered.
Many of those districts are gerrymandered, just not to the extreme shapes we see today. The reason is computers.
Computers and their databases were just moving into the corporate world; one of my college classmates interned with a company to help interpret customer usage data, since no one on staff understood it. Government officials were even less familiar with computers except as tools for the defense and space industries. GIS was in its infancy and was primarily an academic endeavor.
As computers and GIS became more powerful and more accessible to political staffs, the ability to line up political results and demographic groups became easier. That allowed partisan interest to sculpt districts with more precision to get specific results. Those districts are more obviously gerrymandered to look at then these from the 1970s.
Could you give some examples of gerrymanders on that map?
The neighboring, heavily Republican cities of Midland (Midland County) and Odessa (Ector County) are split into different districts to help prevent any of the West Texas districts from being winnable for Republicans.
They were both in the 19th district, were they not? Heavily Republican Lubbock was put there too. There was no reason why Republicans shouldn’t have won that district in 1978. Even Gerald Ford got 58% the vote there in 1976 against Southerner Jimmy Carter.
It looks like Odessa was stuck in with the El Paso centric 16th at the time.