These numbers are for 2007 (I didn't make these maps, by the way. A hardworking intern did). If you add up all counties, the total will be far below the official export total for the state. Why?
This is really company information. What we are looking at is this:
Total waterborne shipment values for all the exporting companies in each county.
Now, not all exporters will be represented here because 1) this shows us waterborne exports while most of our stuff goes to Mexico and Canada via interstate; and 2) many goods are consolidated for shipment in other states by the freight forwarders so the products are counted toward another location, probably a port. As a matter of fact, some large exporters often and purposefully export their products in such a way that they are difficult to track.
So this doesn't tell us much about the movement of state-produced goods. But its still instructive because it does tell us something about our local exporters and how they ship.
Here are some other counties...
UPDATE: You may have noticed the low number for Grady county and, like me, wondered about such a low dollar figure showing up in export data. Perhaps the fine blogger over at Okiedoke has found the answer :)