The department is directed to cooperate with and assist any federal aeronautical agency in the preparation and annual revision of the national airport plan and to lay out a comprehensive state system of airports adequate to provide for the aeronautical needs of the people of all parts of the state. Such state system shall include every airport on the national system and such additional airports as may be deemed necessary. In selecting the general location of the airports on the system and determining their capacity, due regard shall be given to aeronautical necessity as evidenced by the population of the locality to be served, its commerce and industry and such other factors as the department deems pertinent. In selecting the specific sites, due regard shall be given to general suitability for service and economy of development as evidenced by convenience of access, adequacy of available area, character of topography and soils, freedom from hazards and obstructions to flight and other pertinent consideration.