Mapping Software and GIS Glossary

DEFINITION

What is a Splitline Algorithm?

The Splitline Algorithm is a mathematical approach to redistricting that aims to eliminate the element of choice from the redistricting process. Districts are drawn by rigorously applying a recursive algorithm that finds the shortest line that divides a given area into two equal parts.

The algorithm is as follows for dividing a state into N districts:

  1. Start with the boundary outline of the state.
  2. Let A = [N/2], B=[N/2]
  3. Among all possible dividing lines that split the state into two parts with population ratio A:B, choose the shortest. (Notes: since the Earth is round, when we say "line" we more precisely mean "great circle." If there is an exact length-tie for "shortest" then break that tie by using the line closest to North-South orientation, and if it's still a tie, then use the Westernmost of the tied dividing lines. "Length" means distance between the two furthest-apart points on the line, that both lie within the district being split.)
  4. We now have two hemi-states, each to contain a specified number (namely A and B) of districts. Handle them recursively via the same splitting procedure.

Advantages:
- Limits the ability to redistrict in a partisan fashion

Disadvantages:
- Cannot take into account Communities of Interest
- Will most likely not create Minority Majority districts.

These issues make it unsuitable for the majority of states since consideration of Communities of Interest is necessary.

Software for Redistricting

Maptitude for Redistricting is the easy to use, professional tool for political redistricting that can handle all of the intracacies of redistricting including Communities of Interest.

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