Reporting health data for large urban areas presents numerous challenges.  In the case of Toronto, Ontario, amalgamation in 1998 merged six census subdivisions into one mega-city, resulting in the disappearance of standard reporting units.  A population-based approach was used to define new health planning areas.  Census tracts were used as building blocks and combined according to residential income homogeneity, respecting natural and man-made boundaries, forward sortation areas, and the City of Toronto's community neighbourhoods, whenever possible.  Correlations and maps were used to establish area boundaries.  The city was divided into five major planning areas that were further subdivided creating 15 minor areas.  Both major and minor areas showed significant differences in population characteristics, health status, and health service utilization.

This commentary demonstrates the feasibility and describes the outcomes of one method for establishing planning and reporting areas in large urban centres.  Next steps include the further generation of health data for these areas, comparisons with other Canadian urban areas, and application of these methods to recently announced Ontario Local Health Integration Networks.  These areas can be used for planning and evaluating health service delivery, comparison with other Canadian urban areas, and ongoing monitoring of and advocacy for equity in health.