How are the US West, US Central and US East regions divided?

Amazon sellers in the United States often encounter different FBA warehouses. Then when sending FBA headway logistics, the freight forwarder will ask, where your goods are sent to the United States or that area. The United States is generally divided into three parts: the U.S. West, the U.S. Central, and the U.S. East. According to different regions, the distance is different, the shipping time and price is also different. How to divide the U.S. West, U.S. Central, and U.S. East?

U.S. West (states with zip codes beginning with 8 or 9)
Abbreviated as the U.S. West, near the Pacific Ocean, the U.S. West region in the mouth of the freight forwarder is the U.S. zip code beginning with 8, 9 begins with the state belongs to the U.S. West. The two largest ports in the US West are Los Angeles and Long Beach, and the FBA shipping companies generally unload containers at these two ports, such as Mason, Star Clipper, EMC Evergreen and Duffy.

Due to the closer distance, the time efficiency will be faster and the shipping cost will be cheaper. U.S. air freight direct flight is to the U.S. Los Angeles Airport (LAX), and then sent by UPS, Fedex to the U.S. West FBA warehouse, called the U.S. FBA air dispatch.

The central region of the United States (zip code 4, 5, 6, 7 beginning of the state)
The largest city in the United States is Chicago, and our overseas warehouse is in Chicago, and the unpacked container in the United States is the West Coast, and then the unpacked container is transported by rail and waterway to the overseas warehouse in Chicago, and then sent to the FBA warehouse in the United States.

Dallas unpacking sea card is also the same, in Dallas warehouse unpacking by truck after dispatch to the central U.S. FBA warehouse.

Eastern region of the United States (states with zip codes beginning with 0, 1, 2, 3)
The eastern region is relatively far away, so the time limit is longer no matter by air or sea, and the price will be more expensive than the western and central regions of the United States. And because the population in the eastern region is relatively dense, relatively prosperous, and the human union is relatively high, the price of overseas warehouse in the U.S. East will also be relatively high.

FBA shipping to the U.S. East warehouse has two programs, one is to take the east line, that is, from the port of New York port, New York overseas warehouse unpacking and then dispatched by truck. The time limit is relatively slow, and the price is relatively low. There is another kind is the U.S. West express card, in the U.S. West overseas warehouse unpacking, directly by truck to the U.S. East warehouse. The time will be faster, the price is relatively higher.