A New Approach For Geocoding Postal Code-Based Data in Health Related Studies
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Geocoding involves the conversion of textual addresses or names of places into digital coordinates. Health researchers often use geocoding for studying the spatial distribution of populations based on a certain health outcome. To conduct any form of geocoding, health researchers generally require the use of address based data (e.g. street addresses) that are commonly obtained through survey questionnaires or hospital registries. Due to Canadian privacy and confidentiality laws, high precision addresses must be masked or aggregated to coarser geographies. In Canada, most health studies adopt the use of postal codes as they are widely available and accessible. Traditionally, postal codes are geocoded based on the Statistics Canada geocoding methodology that links postal codes to geographic representation points. However, this approach can lead to bias results in accessibility or spatial pattern analysis studies as postal codes (particularly those in rural areas) are at times displaced at far distances from actual residences. As a result, this research introduces a new postal code geocoding approach that can potentially improve upon the traditional approach by considering the land-use within postal code boundaries. Using two study areas (City of Kingston and the province of Ontario) the new and traditional approach were compared to determine which of the two better represents populations (based on residential location) at the postal code geography. Results showed that the new approach significantly improved how populations are represented in rural areas, with minimal improvements for urban areas. The impact of the new approach was also examined using population accessibility to medical clinics in the City of Kingston. The level of impact was based on the amount of population that was misallocated (by the two approaches) to non-nearest medical clinics. No significant difference was found in results between the two approaches with the new approach misallocating approximately the same amount of population (at both urban and rural areas) as the traditional approach. A larger study area that incorporates a higher number of rural postal codes is suggested (where the new approach has a higher geocoding positional accuracy) for future research.