Once a database has been prepared, the next step in the redistricting process is the formation of districts. This is the step in which the line drawers create a redistricting plan either by assigning geographic units to districts for the first time or by moving geographic units in an existing plan from one district to another. A redistricting plan is complete when all geographic units in a given territory are assigned to a district and all districts in the plan meet the predetermined redistricting criteria. The geographic units to be assigned may be as large as counties or cities and towns, or they may be smaller units of geography such as census blocks or voting areas.
If the line drawers are to create a new redistricting plan by modifying districts in an already existing plan, their tasks may be relatively straightforward. This is especially true if a decision has been made that districts should be modified only as much as necessary to meet equal population standards. Many countries, for instance, list consideration of existing district boundaries as a redistricting criterion. If there is no existing redistricting plan to modify or if the number of districts in an existing plan is to change substantially, the line drawers' tasks become more challenging.
Modifying Districts in an Existing Plan
One strategy that could be adopted if districts already exist and simply need to be modified is to (1) determine the current population of each of the existing districts, (2) calculate the minimum amount of change required to meet equal population standards, and (3) focus only on the districts that need to add or subtract population. Of course, it is never as simple as adding or subtracting population only from the malapportioned districts. Since the process also affects adjoining districts, a ripple effect usually occurs across the districts, necessitating at least some changes to other districts. But an effort could be made to minimise these changes.
This incremental approach to redistricting is often adopted by line drawers who are required to consider existing district boundaries when redistricting. It may also be a good strategy if the legislative body for which new districts are being drawn must approve the redistricting plan before it can be implemented. The chances of obtaining legislative approval for a redistricting plan are obviously affected by the extent to which existing districts are disrupted. In the United States, for example, the wisest strategy is often to move only the minimum amount of geography necessary to achieve population equality – this ensures bipartisan legislative support for the redistricting plan.
Creating a New Plan or Substantially Modifying a Plan
Drawing districts where districts have not previously existed or where district boundaries must be changed substantially is a more complex process. The task of drawing districts for the first time can be simplified by dividing a large territory into manageable sub-regions and drawing districts in two or three stages. If a country is divided into states or provinces, for example, allocating districts first to the states or provinces and then drawing districts within these states or provinces will make the process more manageable. A second level of district allocation may also be desirable if the states or provinces are large. If further allocations are made, however, the subdivisions should possess some sense of geographic unity.
Choosing the Basic "Building Block"
One of the first decisions to make in creating districts is what unit of geography and, possibly, what level of geography to use as the basic building block. This decision is required whether the line drawers are to modify an existing districting plan or create an entirely new plan. Whether composed of census or election geography, the redistricting database has, presumably, been built upon a unit of geography small enough to give the line drawers some flexibility in creating districts.
The line drawers, however, need not use the smallest unit of geography available in the redistricting database as the only building block when creating or modifying a plan. For example, redistricters may be able to assign whole counties or cities in many areas and resort only to individual census blocks or voting areas in certain, usually urban, areas. And, in fact, it is easier and faster to create the broad outlines of districts with large geographic units and then use the smaller units to make the refinements necessary to comply with equal population standards or other redistricting criteria.
Choosing Where to Begin Drawing Districts
Another decision that should be made early in the process of creating districts is where to begin drawing district lines. Redistricters often begin at the corners of a territory and work towards the centre. This is done to avoid any distortion which may result at a corner or edge if the process starts at one side of the territory and moves to a final corner or edge.
There may be reasons to begin the line drawing elsewhere. If, for example, the redistricters wish to create a district for a geographically concentrated minority community or some other community of interest, they may begin by drawing the boundaries of that particular district and then move the line drawing process outward from that district.
Drawing District Boundaries Interactively
Once decisions have been made about what units of geography to use as building blocks and where to begin the line drawing process, the actual line drawing can commence. The line drawing process is an interactive one. The redistricters assign a piece of geography and then determine how the inclusion of that particular geographic unit affects the size and composition of the district.
Although aggregating the population totals for the districts after each new assignment is a straightforward process, it can be a tedious one as well. And as geographic units continue to be shifted, this process is repeated over and over again. A computer can automate this process, but it can also be done manually with a hand-held calculator, if necessary.
