From Precinct to Voter [...]

Early political processes focused on precincts and wards as the unit of allocating campaign effort. You would get out the vote in the areas where you had broad support, and sometimes, less honorably, suppress the vote in those places where you didn’t.

As canvassing became supplemented with phone calls, direct mail, and other pieces, the unit increasingly became the individual voter. Campaigns were less concerned about getting out the vote of Ward 8 and more concerned about flushing out demographics such as “College educated under-25s”

As early as the 1960s Democrats began systematically assessing which precincts should be allocated campaign resources using statistics aggregated over fairly wide geographic areas. By the 1990s, the precinct was being supplanted by the individual voter as the unit of analysis, just as wall maps and clipboards were giving way to web applications and Palm Pilots. (Source)

As campaigns became more focused on these units of analysis, many traditional GOTV efforts became less privileged. And even where traditional methods were used, they were used under the guidance of the new approach — a ward captain in 1960 would get out the vote for his or her ward; by the 2000s they would be armed with data on what specific doors they needed to knock on, based on likely percentages of support and number of previous touches tracked.