Alex Reisner has made the observation that baseball parks are built differently depending on whether they are located in an urban or rural area. Further:
Professional baseball teams must play in places where fans can go to see them. Before the 1950s this meant that they played in cities where the population was dense and public transportation available. In the 1950s, however, as cars became affordable and good roads the rule rather than the exception, the growing class of car owners began to move to the suburbs. It was no longer necessary to locate a ballpark in the city, and it became common practice to build on the outskirts where land was cheaper, parking safer, zoning rules more lax, and events generally less disruptive.
He notes that ballparks built after 1960 when personal transportation was more widely used are more symetrical and larger, while the shape of ballparks built before that time are often irregular and smaller so they fit into a city center. Look at the New York Mets’ Shea Staduim on the left and the Boston Red Sox Fenway Park on the right below.