Redistricting is the process of assigning map objects to groups. As you assign map objects to groups, MapInfo Pro automatically calculates totals for each group of objects, and displays the totals in a special Browser window called the Districts Browser. This process is sometimes known as load-balancing.
When you perform redistricting, you create a number of districts. The exact number of districts needed depends on the nature of your work. You can assign a unique name to each district; thus, if you want to work with four districts, you might call the districts Northeast, Southeast, Northwest, and Southwest. Each district appears as one row in the Districts Browser.
The Districts Browser is different from other Browser windows in several respects:
- You only can select one row at a time from the Districts Browser. You cannot Shift-click to select multiple rows.
- The Districts Browser always has one row selected; you cannot cancel the selection of this row by choosing the Clear command.
- When you select a row from the Districts Browser, that row becomes the target district. The target district is the district that will be affected by subsequent redistricting operations.
Once you have selected a target district, you assign map objects to that district by selecting the map objects. You can select objects by pointing and clicking, or by performing queries such as SQL Select.
When you select map objects, MapInfo Pro tentatively assigns the selected objects to the target district. MapInfo Pro then recalculates the totals for each district, and displays the new totals in the Districts Browser. You can then examine the contents of the Districts Browser to decide whether you want to make the district assignments permanent.
To cancel the tentative district assignment, cancel the selection of the map objects.
To make the tentative district assignment permanent, on the MAP tab, in the Options group, click Redistricter, and Assign District. When you choose Assign District, MapInfo Pro stores the target district's name in the rows of the selected objects. Thus, if you assign map objects to a district called Northwest, MapInfo Pro stores Northwest in each object's row.
Each district has its own set of fill, line, and symbol styles. When you assign a map object to a district, the object subsequently appears in the style of the district. Thus, if you choose a solid blue fill for the Northeast district, objects that you assign to Northeast appear in solid blue.
For example, if you have a layer of states, you might want to combine the state boundaries to create sales territories. Each state record includes a field, TOT_SALES, which contains the total sales for the previous year. You would ultimately like to sum up the TOT_SALES field for each state in a given sales territory. Redistricting is gives you the tools for creating the sales territory and combining those TOT_SALES fields from each state's data into one table.
But that is only one part of the redistricting process. The real power lies in the Districts Browser where you can see on-the-fly updates of district record counts and data totals when you click a map object and assign it to another district. This allows you to perform visual "what if" analysis to achieve district realignments, a process sometimes referred to as load balancing.
When you are satisfied with the distribution, you can make the district assignments permanent. Later, as the need arises, you can change the assignments and try out new distributions.
Redistricting does not create new map objects or permanently change the style of the map objects. Redistricting is simply a dynamic grouping tool that displays map objects that share the same district information as a group. While the map objects are not permanently affected, you can make the district assignments permanent by saving the table.
You can redistrict any mappable table containing region, line, or point objects. The redistrict map will reflect the appropriate fill, line, or symbol style for the objects. The Redistricter limits the number of districts in a table to 594.
You can use redistricting in a wide variety of applications such as creating and managing sales territories, school or voter districts, emergency service coverage areas, delivery routes, natural resource management areas, etc. Use it wherever there is a high degree of fluctuating data and the need to try out different realignment scenarios.
You can use redistricting whether you need to create districts from scratch or realign existing districts.
Before we get into the process, however, there are two key concepts to introduce: the Districts Browser and Target District.