In this page, it shows three maps. The first is about all airlines departing from Putong International Airport, Shanghai, classified by airline companies. The second is about the same airlines, classified by flying distances. The third shows the degree of drought around USA.
In this map, I choose Pudong International Airport (PVG), Shanghai, because I usually departed and arrived there in my undergraudate life. In this map, it shows all airlines with the same oringin from PVG. Each line is managed by an airline company, which is shown by using different colors and labels. Besides, some lines are not looking straight because of the curve of earth. Note that the lines don't mean the real air routes, many factors are taken into consideration during the design of an air route.
Most of the contents in this map have the same meaning with the above map. The difference is colors here means different flying diatances. In the sql, the key sentence is "(ST_DistanceSphere(ST_Transform(oringin,4326),ST_Transform(arrival,4326))) AS dis". The darker the color is, the greater the distance is. The realistic distances are the numbers on the legend multiplied by 1000km.
In this map, it generally shows the distribution of drought over USA. Colors show the drought level. The drier a place is, the reder it shows. The category uses Jenks classification method. The data is from US Drought Monitor on 12/29/15.