In the supreme court determined that purposefully drawing districts where the majority of voters were members of a single minority group, in order to ensure minority representation, was unlawful.

Reno vs Shaw
  the residents of North Carolina appealed to the supreme court when the attorney General rejected their plea. They had also taken the case to the district courts and the courts had ruled against the decision. Redistricting based on race was the main motive behind the rejection.

The answer is professionals such as attorneys.