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mapping methods

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  • For each data source, information about data collection and analytical methods, limitations, the citation and additional resources can be found on the Data Sources and Methods page.


  • Peel Health Services employs either ESRI's ArcMap (v10) or Intergraph's GeoMedia (v6.1) mapping software to present health data in a visual, "spatial" representation.
  • The purposes of mapping health status data are to assist us to better understand our population and make better decisions regarding policy and planning.
  • Health status data need to have some geographic information contained in the file in order to be able to map them. This could take the form of a 6-digit postal code, a 3-digit Forward Sortation Area (FSA), a Census Tract (CT), the municipality name or Census Sub-Division (CSD), the region name or Census Division (CD), or some other geography such as the Peel Data Zone (DZ).
  • When the 6-digit postal code is available in health data, it can be converted to a Census Tract using a software tool called the Postal Code Conversion File (PCCF). Once converted, events of interest (e.g. births, deaths, hospitalizations, Emergency Department Visits) can be summed based on that level of geography, and used in the numerator of rates or proportions.
  • Population estimates data used in the denominator of rate calculations prepared for maps most often come from the Census, using the straight line method of estimating the population in a given area from the 2001 and 2006 Censuses, forward to 2010.


  • Rates are calculated by dividing the number of events of interest in the geographic area by the sum of the population in that same area, then multiplying by a factor of 100, 1,000 or 100,000, depending on the rate being shown. Depending on the data source, the rates that used to present data in the maps could be crude rate or age-standardized.
  • Age-standardized rates for data zones are calculated using the 1991 Canadian population using a straight line estimate of the 2006 population up to 2010 as the denominator, and using the direct method of standardization.
  • Most maps on the Peel Health Data Web Site are thematic maps that indicate whether a smaller geographic area's rate is different from or the same as that of Peel. Methods used to compare a smaller geographic area to Peel as a whole depend on the source of the data shown on the map.
Presentation of Census Data:
  • All Census data are presented by CT or DZ.
  • Rates are first calculated for Peel, and by CT or DZ.
  • Rate Ratios are calculated using the area's rate as the numerator and Peel's rate as the denominator. The rate ratio is then divided into three categories for mapping: less than or equal to 0.80 ("<=0.80"), indicating that its rate is 20% or more below the Peel average; between 0.81 and 1.19 ("0.81-1.19"), indicating that its rate is the same as the Peel average; and greater than or equal to 1.20 (">=1.20"), indicating that its rate is 20% or more above the Peel average.
Other Health Data (Hospitalizations, Emergency Department Visits, Deaths, Stillbirths, Live Births, and Survey data from the CCHS):
  • All other health data are presented by CT or DZ.
  • Rates and 95% Confidence Intervals are calculated for Peel, and by CT or DZ.
  • Rates of CTs or DZs are compared to the Peel rate and Confidence Intervals are examined to see if they overlap.
  • The CT or DZ is shaded a range of three colours as follows:
  • Light colour if its rate is significantly below the Peel rate (the confidence intervals do not overlap),
  • Medium colour if its rate is similar to the Peel rate (the confidence intervals overlap), or
  • Dark colour if its rate is significantly above the Peel rate (the confidence intervals do not overlap).

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