Abstract

Background

Postal codes are often the only geographic identifier available to match subjects in a health dataset to census geography. This paper describes the characteristics of postal codes reported by the Canadian population on the census and, as an indicator of geocoding accuracy, the proportion that are linked to a single dissemination area (DA).

Data and methods

Postal codes reported on the 2016 Census questionnaire were matched to a combination of the Postal Code Conversion File (PCCF) and the Postal Code Conversion File Plus (PCCF+ version 7B) (reference date November 2018) to calculate population-weighted counts and the number of matches to DAs by province or territory, delivery mode type (DMT), population centre or rural area size, and census metropolitan area. The number of single matches to census tracts (CTs), census subdivisions (CSDs) and census divisions (CDs) was also calculated.

Results

In Canada, 72.6% of the population reported postal codes that matched to a single DA. This proportion was higher in urban cores (87.1%) and among postal codes for an urban street address (DMT=A) (85.3%) or apartment building (DMT=B) (95.3%), and was lower in rural areas (26.2% to 38.1%) and among rural postal codes (13.9%). In comparison, 89.3% and 95.4% of the population reported postal codes matching to a single CSD or CD, respectively, while 92.1% of the population that live within CT boundaries were matched to a single CT.

Interpretation

Matching postal codes to census geography is relatively accurate and frequently one to one in urban centres. In rural areas and for some types of postal code DMTs, alternative approaches to using the PCCF and PCCF+ for attaching census geography might be explored.

Keywords

postal code, Postal Code Conversion File Plus (PCCF+), delivery mode type, geocoding, geography

DOI: https://www.doi.org/10.25318/82-003-x202000300001-eng

Findings

In the majority of Canadian health survey or administrative datasets, the geographic information available to researchers is limited to a residential postal code rather than a full street address, often for confidentiality reasons. Postal codes are six-character alphanumeric codes created by Canada Post Corporation to sort and deliver mail. Since postal codes do not always reflect well-defined, discrete and homogeneous spatial units, there is some uncertainty in using them to assign geographic attributes, such as exposures to environmental hazards. Postal code geography also does not always correspond with census geography, since many postal codes cross census boundaries. Therefore, postal codes may be linked to one or more units of census geography. [Full article]

Authors

Lauren Pinault (lauren.pinault@canada.ca) and Michael Tjepkema are with the Health Analysis Division and Saeeda Khan is with the Social and Aboriginal Statistics Division at Statistics Canada in Ottawa, Ontario.

 

What is already known on this subject?

  • Postal codes are often the only geographic identifier available to assign census geography to subjects in a health dataset.
  • The Postal Code Conversion File Plus (PCCF+) provides a means to match postal codes to units of census geography, using population weights.
  • Positional accuracy (latitude/longitude coordinates) in the PCCF+ are most accurate for urban apartment buildings and street addresses.

What does this study add?

  • This study uses postal codes reported on the 2016 Census of Population to determine how frequently postal codes are matched to one unit of census geography in the PCCF+, as a measure of accuracy.
  • In Canada, 72.6% of the population matched to a single dissemination area (DA), 89.3% to a single census subdivision, and 95.4% to a single census tract.
  • Accuracy (match to single DA) was higher in urban apartment buildings and street addresses, and was lower in rural areas.

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