AdMarketplace is adding GPS information collected from consumers' mobile devices to the data that mobile ad networks provide for serving paid-search ads. Experts say GPS tools are more accurate than ZIP codes or Internet protocol address targeting. "GPS coordinates from a phone give you much better information. Starbucks can serve you a coupon while sitting here in front of the coffee shop, and then you'll walk across the street to Kohl's and receive an offer from the retailer. It's that sensitive," said Andries de Villiers, vice president of revenue at adMarketplace.