In the clip, Charlie plots the bombing locations on a map and is able to find the "center" of those points, which is the most likely place the bomber would choose as a base of operations. There are many geometric notions of center of a collection of points in the plane. One obvious one is the point which minimizes the sums of distance from that point to all others. Unfortunately, such a point is often difficult or impossible to find explicitly. This is because the distance between two points involves a square roots, which are difficult functions to analyze.
This clip is based on the true court case, Anderson v. Cryovac, Inc., which involved environmental pollution in Woburn, Massachussetts in the 1980s. The case centered on trichloroethylene, a solvent that had contaminated nearby groundwater and seems to have caused fatal cases of leukemia and cancer. In this scene, the plaintiff's attorney goes back and forth with the opposing party to reach a settlement before the trial begins.