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.
The 19th district was held by George Mahon from 1934-1978 its only representative ever since it was created in 1934. His last 14 years were as chair of the House Appropriations Committee.
He only had a Republican opponent 3 times, the last in 1976 when he won 55-45.
His Democratic successor was Ken Hance, who in 1978 portrayed his young opponent (32 at the time) as a Connecticut Yankee outsider. 16 years later that opponent would become governor, and 6 years after that president.
Hance was a very conservative Democrat, who would carry Reagan's tax cuts. In 1984, he narrowly lost the Democratic nomination for US Senator. In 1986 and 1990 he lost the Republican nomination for governor, though he was elected as a Republican to the Railroad commission.
In the 1984 election to replace Hance, the Democrat got 42% of the vote, one of only two Democrats since then to clear 40% (in 2018, the Democrat got 25%).
It is not clear that the 1970 districts were not drawn simply to balance population. A court decision made the boundaries look a lot worse. In any event, 35K of 91K of Ector County was in TX-19. Generally, the eastern side of Odessa is wealthier than the west side, some of which is not actually in the city (see Saturday Night Lights, the book). Odessa has refinery and was closer to oil production and more working class, while Midland is more management. Until recently, there was not that much production from Midland County, though that has changed somewhat with fracking.
At one time TX-16 reached almost to Fort Worth and has gradually been retracting. Before the 1970 redistricting both