How Remove Trade Area Overlap (Business Analyst) works

The Remove Trade Area Overlap tool removes cannibalization between trade areas generated in Business Analyst or custom derived trade areas. Overlap is removed using Thiessen polygons or a grid based approach to find the midpoint between the intersecting areas.

Remove Overlap Methodology

Assume you have two trade area polygons that have an intersection.

trade area polygons with an intersection

In the example below, the area highlighted light blue represents the overlap area. The two triangle symbols represent the stores for each trade area.

Light blue represents overlap area

The Remove Trade Area Overlap function in Business Analyst is based on the assumption that overlap is only removed by dividing the intersection area. The tool does not assign areas that are not overlapped to other stores. In the example above, only the area that is shaded blue will be affected by the Remove Trade Area Overlap tool.

There are two approaches for removing overlap:

Method 1 - Thiessen Polygon

The Thiessen polygon approach removes overlap between two or more trade areas using straight lines to divide the area of overlap. This approach uses a series of geometric functions to create nonoverlapping trade areas. First, a line is drawn between each store and neighboring store.

Thiessen polygon

Second, a perpendicular line is drawn bisecting the line drawn between the stores at a right angle. The dotted line below is drawn at the midpoint between the two store locations and represents the division between the two trade areas.

Thieseen polygon with division

Method 2 - Grid

The grid approach takes into account weights of the stores and shape of the overlapping polygon to make the division more natural.

The grid approach uses a series of geometric functions to create nonoverlapping trade areas. First, a line is drawn between each store and neighboring store. Second, two parallel lines are drawn that pass through the stores that are perpendicular to the line drawn between the stores. The red shaded area below illustrates the target area of intersection. This area is determined by finding the area of overlap between the two trade areas contained between the two perpendicular lines.

Grid approach

After determining the area of intersection, a grid is created by drawing parallel lines between the two stores. A simplified example is illustrated below.

Grid with parallel lines

Intersection points are then determined within the red area so each grid line can be divided into nonoverlapping trade areas. The yellow points above illustrate how the midpoints are determined. These points are connected to represent the division between the overlapping trade areas.

Grid with intersection points

In the grid approach, there are three different methods for determining where to draw the intersection line. These three methods determine how the midpoints are used to draw a line between the two polygons to remove overlap. Specifically, these three methods determine where the yellow dots are placed to create the nonoverlapping line between the two trade areas.

Grid with overlap
3/3/2014