Canadian Longitudinal Tract Database

Jeff Allen, University of Toronto
jeff.allen@mail.utoronto.ca

Zack Taylor, University of Western Ontario
zack.taylor@uwo.ca

Data:
http://dx.doi.org/10.5683/SP/EUG3DT

Related article:
Allen, Jeff and Zack Taylor. Forthcoming 2018. A New Tool for Neighbourhood Change Research: The Canadian Longitudinal Census Tract Database, 1971-2016. Canadian Geographer.

The Canadian Longitudinal Tract Database (CLTD) enables the spatial apportionment of Canadian census tract-level data from different census years to common geographic boundaries. Apportionment tables were generated for all pairs of adjacent census years starting in 1971, for each year to 2016. Note that 1976 is absent because no digitized spatial data files are available for that year. The tables were generated using a variety of spatial techniques that account for population density and land use. These are described in a forthcoming article accepted by Canadian Geographer. Please contact the authors for more details.

Each apportionment table has four columns:

ctuid_s = source census tract identifier
ctuid_t = target census tract identifier
w = apportionment weight
f = flag indicating relationship between source and target tract

Tract identifiers are in the standard “7.2” Statistics Canada format (0000000.00). The first three digits are the census metropolitan area (CMA) code. The remaining digits (0000.00) identify individual census tract within each CMA. Note that Statistics Canada used two-digit census metropolitan area codes in 1971. After 1976, they switched to three-digit codes. The “cma_code_1971-2016_lookup” table links the two CMA numbering systems. The source tract name column in the 1971-2016 census tract crosswalk table uses the 1971 CMA codes.

The weights range from 0 to 1. Weights pertaining to a given source tract sum to 1. A value of –1 indicates that there is no source due to the creation of a new tract in a previously untracted area, or that there is a no target due to a reduction in tracted territory.

The flags are as follows:

1 = no changes to tract boundaries
2 = merge (multiple source tracts correspond to a single target tract
3 = split (single source tract corresponds to multiple target tracts)
4 = “many-to-many” relationship

Using the tables
Using the crosswalk files is straightforward. First, obtain census tract-level data from Statistics Canada or other sources. Join that data to the crosswalk table on the standard source tract identifier (ctuid_s). Multiple your source data by the weights (w). Finally, “collapse” or “group” the table on the target tract identifiers (ctuid_t) so that there is one row for each target tract, summing count data.

Non-count data that represent means, ratios, or percentages require additional pre-processing. Examples include average household income, percentage below low-income cut-off, or unemployment rate. In these cases, values must be converted into counts by multiplying them by the appropriate denominator in the source file. Variables representing medians cannot be apportioned because the underlying distribution of values in the population is unknown.

Finally, note that tract relationships only exist in areas tracted in the source year. We recommend exploratory mapping to ensure that the phenomenon of interest falls within the area covered by the apportionment tables.

8 April 2018