Larger district magnitudes means larger districts, so annihilate the need and practice of gerrymandering, Gerrymandering is the practice of partisan redistricting by means of creating imbalances in the make-up of the district map, made easier by a multitude of micro-small districts. A higher magnitude means less wasted votes, and less room for such maneuvers. As well, a fair voting system in the district contests also means that gerrymandering is ineffective because each party gets their fair share of seats however districts are drawn, at least theoretically.
