As soon as the end of the year, Twitter is planning to let brands show promoted tweets to people who open its mobile apps within close range of their stores. Twitter will enable ads to be targeted to people who are near specific latitudes and longitudes and could be ready as soon as the fourth quarter, according to two people briefed on the product. This kind of radius-based geo-fencing could potentially be useful for the likes of a pharmacy chain like Walgreens or even a quick-serve restaurant like McDonald’s. It’s for marketers who are looking to drive up their in-store traffic with the carrot of a deal or a special, or just by tipping people off to their presence in the immediate vicinity. Though a release at the end of the year would make the product available for holiday retailers — a potentially lucrative customer base — it also seems subject to delay.