Frankford Yellow Jackets - Wikipedia
run + travel: Postcards from Philadelphia (guest post)
John F. Kennedy Stadium (Philadelphia) - Wikiwand
Veterans Stadium - history, photos and more of the Philadelphia Phillies former ballpark
Then and now: a historic look at Philadelphia's ballparks
Stadiums and Arenas - Encyclopedia of Greater Philadelphia
Then and now: a historic look at Philadelphia's ballparks
Shortstops: A Map of the Park
Philadelphia and Its People in Maps:The 1790s - Encyclopedia of Greater Philadelphia
Topographical map of Fairmount Park, Philadelphia - Norman B. Leventhal Map & Education Center
The Jefferson Street Ball Parks (1864–91) – Society for American Baseball Research
Then and now: a historic look at Philadelphia's ballparks