A systematic approach to evaluate and validate the spatial accuracy of farmers market locations using multi-geocoding services

The USDA National Farmers Market Directory is the largest and most comprehensive directory of farmers markets in the United States. It is the only farmers market directory that provides the geographical coordinates of market locations and allows the public to download the dataset at no cost. The geographic coordinates of the market locations in the directory were collected through a web-based GIS data collection form. This form allows market managers to navigate, review, and adjust market locations on the web-based map, and to save the coordinates of the market locations into the database. However, market location addresses and descriptions provided by users are in an open-ended format, which did not allow automatic verification of the accuracy of a market location. In using the web-based GIS to capture market coordinates, deficiencies in users' computer literacy skills, attention to details, Internet speed, etc. means spatial errors in market locations coordinates were possible. Hence, the directory data, including market location coordinates, has to be validated before it is delivered to the public. This study developed a method to verify the coordinates of farmers market locations by comparing user-generated market coordinates against the geocoded coordinates from multiple geocoding services based on user-submitted market addresses. Using the USDA 2012 National Farmers Market Directory as a test dataset, three-quarters of the market locations generated by farmers market managers were verified as the ground-truth locations. This study suggests that multiple geocoding services provide a feasible and practical method for validating user-generated farmers market locations. (C) 2013 Elsevier Ltd. All rights reserved.