The older maps:

• Followed the federal Apportionment Act of 1911 requiring that congressional districts be
  “… contiguous and compact territory …” with an
  “… equal number of inhabitants.”
• Resisted engaging in overt partisan gerrymandering.
• Included adjustments to favor or disfavor individual legislators.

Since 1968:

• The Pennsylvania constitution requires an additional rule:
  “ … [u]nless absolutely necessary no [political boundary] shall be divided … in forming either a senatorial or representative district.”
• Explicit state constitutional rules apply only to state senate and representative districts.
• However, the Pennsylvania Supreme Court later ruled that constitutional requirements must apply to Congressional redistricting to ensure free and equal elections.

More recently:

• Amanda Holt, a voter and self-taught mapper, challenged the 2011 state representative map, leading to an improved 2012 state legislative map.
• The League of Women Voters of PA challenged the 2011 congressional map in a 2018 lawsuit, resulting in the Pennsylvania Supreme Court’s invalidation of the map and installation of the 2018 remedial map.