[3] Delimitation or redistricting is the process of drawing congressional boundaries and can also refer to the demarcation of voting areas for the purpose of assigning voters to polling places.
Manipulation of this framework often results in gerrymandering, the practice of drawing district boundaries to achieve political advantage for legislators.
[9] This has resulted in unequal representation in districts such as Calacoon City, and Batanes being represented by one legislator each, despite containing populations of 1.2 million and 17 000 people respectively.
As incumbents control the institutions that determine the rules for redistricting, many of the congressional districts are allegedly gerrymandered to ensure the elite persistence of select families that form the Philippines' political dynasties.
[15] The boundaries and numbers shown for the congressional districts are established by their respective state's constitution or court orders in the apportionment and redistricting cycle.
[21] These methods have been the subject of debate for over 200 years as losing or gaining a seat affects representation which is the source of political power.
The redrawing of boundaries occurs after the decennial census; single-member constituencies are responsible for the election of the legislators that govern this process.
[24] Each state has its own constitution and laws surrounding the redistricting process, and most of the modern criteria applied federally have come about through rulings by the U.S. Supreme Court.
[26] Since Shaw v. Reno (1993) and Abrams v. Johnson (1997), the courts have invalidated numerous congressional redistricting plans upon the basis of traditional districting principles.
[27] According to the database of redistricting laws in all fifty states and previous court decisions, the de facto principles are: compactness, contiguity, equal population, and preserving county and city boundaries.