For the purpose of the better administration of the department, the commissioner of commerce shall divide the counties of the state into as many districts for the purpose of supervision as may be practical, taking into consideration the volume of work represented and the number of examiners or assistants available, and shall also designate the district in which each of the examiners or assistants appointed under the provisions of section 46.08 shall make examinations. In arranging the districts, the commissioner of commerce shall also consider the matter of convenience and economy as much as possible in covering the same by examiners.