If you zoom in you can see their name. Couple of names I picked up, are ware houses and distribution centers for ebay, wallmart, petsmart to name a few. The reason Gigafactory doesnt look as impressive compare to others because only 15% of GF construction has been done so far (according to Bloomberg Article). So the completed structure will easily dwarf everything else in the vicinity.

If you look at the corners of the plot, you can see the short sides of the octagon that the completed building will eventually become.

Overlaid on the financial district of New York, for comparison: http://mapfrappe.com/?show=39101