Geocoding to Create Survey Frames

Abstract

With the Delivery Sequence File (DSF), from the United States Post Office, surveys can cheaply and easily create address frames and samples. Many studies have examined the coverage of these frames (see e.g., Dohrmann et al. 2006; Iannacchione et al. 2003; O’Muircheartaigh et al. 2002). However, these studies do not discuss geocoding. Geocoding is a key step in turning the DSF into a survey frame. Survey researchers who use these frames should understand the role geocoding plays, whether they do this work themselves or buy already-geocoded frames or samples. Geocoding is necessary because there is a mismatch between the geographies on the DSF and those used in most surveys. The DSF contains only street address, city, state, zIP code, and other fields related to mail delivery. Household samples, however, are often based on census geographies such as counties, tracts, and blocks. Geocoding translates the address data into census blocks. We have learned a lot about the geocoding process over the past ten years of work with the DSF. In this article, we share what we have learned. We explain what geocoding is and how it works. We also discuss what can go wrong. Geocoding is a two-step process. First an address is assigned a geographic coordinate (usually latitude and longitude). Then the coordinate is mapped to census geography. All addresses placed in tracts or blocks selected for the survey are part of the frame.1