As i can get the zipcode from
"sashelp.zipcode" and also from the website of SAS company.
Alot of zip code is available for the whole U.S area, and the same time the centor of the zipcode's latitude and longitude is also available from that data source..
As i wish to gain the distance between each zipcode and the zipcode of the CBD (Commerical business district). However, i can not find and determine which zipcode is for the CBD of all the cities, so even i know the equations for the distance, i still can not get the distance.
where can i get the U.S. Cities'CBD zipcode file? so i can match it and then calculate the distance.