Geography in Ontario

The Standard Geographical Classification (SGC) is a system of names and codes representing areas of Canada.¹ It consists of a three-tiered hierarchy - province or territory, census division, and census subdivision. Lower levels of Census geography such as Census Tracts (CTs), Enumeration Areas (EAs) prior to 1996, and Dissemination Areas (DAs) from 2001 onward, are less commonly used for collection of health data but can be used for analysis based on recoding from the postal codes (see later discussion of postal code system). CTs, EAs and DAs are available for Census data² and can be useful for regrouping into some level of geography lower than the CSD level for "community level" analysis. Most data produced by Statistics Canada uses this system including Census data, population estimates and projections.

The Ontario Ministry of Health and Long Term Care (MOHLTC) bases all geography on the MOHLTC Residence Coding System. The lowest level (4 digits) represents municipalities, townships, named settlements, First Nations Reservations, and unorganized areas. These geographic units are the basis of the Public Health Unit geography. Most data coming from Statistics Canada, including population estimates and projections and vital statistics must be regrouped into Residence Codes based on Census Sub Division (CSD). Because some CSDs map to more than one Residence Code, decisions regarding the assignment of CSDs to unique Residence Codes are made by the MOHLTC. Residence Codes reflect changes in the municipal boundaries that occur between Census years whereas Statistics Canada’s data is based on CSDs from the most recent Census.

The next highest level of geography for MOHLTC is the county/district. Counties are created by grouping 4-digit Residence Codes together and therefore differ somewhat from Statistics Canada’s Census Divisions (based on groupings of CSDs). In many cases these geographies match; most differences are related to where First Nations Reservations are placed. Statistics Canada splits Reserves across CDs whereas MOHLTC selects one county to place the entire reserve.

In many cases public health units consist of either single or groups of counties or CDs, however, in some cases (marked with an asterisk in Table 1 below) a CD will fall into more than one health unit area. (see map of Ontario Public Health Unit and County Boundaries) For this reason, when aggregating data which is based on census geography, it is preferable to group CSDs rather than CDs into health units. Some current health units are a result of past amalgamations of health units, these are highlighted in Table 2 below. As of June 2006, there are 36 public health units in Ontario.

*Indicates census divisions which fall into more than one health unit area.

The highest level of geography in the MOHLTC's system is the Health Planning Region. The boundaries of these regions differ from those for other Ontario Ministries such as the Ministry of the Environment and the Ministry of Community, Family and Children's Services. The MOHLTC has seven Health Planning Regions (Central East, Central South, Central West, East, North, South West, and Toronto) which replaced the five previous regions (Central East, Central West, South West, North and East) in 1998. These previous five regions also coincided with the five Health Intelligence Units (HIUs) which were in existence in Ontario between 1996 and March 2005.

Another level of geography used by the MOHLTC was that of the 16 District Health Units (DHCs). The DHCs were disbanded in March 2005.

Local Health Integration Networks (LHINs) were established in 2005. LHINs are non-profit organizations that are designed to plan, coordinate and fund the delivery of health care services across the province. Though the LHIN boundaries do not coordinate well with all existing Public Health Unit boundaries, they do provide another geographic unit for analyzing health data. Table 3 below shows the LHINs by Public Health Unit. (see map of LHIN boundaries http://www.health.gov.on.ca/transformation/lhin/lhinmap_mn.html)

TABLE 3: Local Health Integration Network (LHINs) by Public Health Unit (PHU)

LHIN Name	PHU Name
Central East	Durham Region Health Department Haliburton, Kawartha, Pine Ridge District Health Unit Peterborough County-City Health Unit Toronto Public Health*
Central West	Regional Municipality of Peel Health Department* Wellington-Dufferin-Guelph Health Unit* Toronto Public Health* York Region Health Services Department*
Central	York Region Health Services Department* Toronto Public Health* Simcoe Muskoka District Health Unit*
Champlain	City of Ottawa – Public Health and Long-Term Care Branch Eastern Ontario Health Unit Renfrew County and District Health Unit* Leeds, Grenville and Lanark District Health Unit*
Erie St. Clair	Chatham-Kent Public Heath Services County of Lambton, Community Health Services Department Windsor-Essex County Health Unit
Hamilton Niagara Haldimand Brant	Brant County Health Unit City of Hamilton – Public Health and Community Services Department Regional Niagara Public Health Department Haldimand-Norfolk Health Unit* Halton Region Health Department*
Mississauga Halton	Halton Region Health Department* Regional Municipality of Peel Health Department* Toronto Public Health*
North East	Algoma Health Unit North Bay Parry Sound District Health Unit Sudbury and District Health Unit Timiskaming Heath Unit Porcupine Health Unit* Renfrew County and District Health Unit
North Simcoe Muskoka	Simcoe Muskoka District Health Unit* Grey Bruce Health Unit*
North West	Northwestern Health Unit Thunder Bay District Health Unit Porcupine Health Unit*
South East	Hastings and Prince Edward Counties Health Unit Kingston, Frontenac and Lennox and Addington Health Unit Leeds, Grenville and Lanark District Health Unit*
South West	Oxford County Board of Health Elgin St. Thomas Health Unit Huron County Health Unit Middlesex-London Health Unit Perth District Health Unit Grey Bruce Health Unit* Haldimand-Norfolk Health Unit*
Toronto Central	Toronto Public Health*
Waterloo Wellington	Region of Waterloo Public Health Wellington-Dufferin-Guelph Health Unit* Grey Bruce Health Unit*

*Indicates public health units which fall into more than one LHIN area.

The Canadian postal code is an alpha-numeric combination of six characters describing the destination of each item of mail addressed in Canada³. The characters are arranged in the form "ANA NAN" where "A" represents an alphabetic character and "N" represents a numeric character (e.g. K1A 0T6). The first character of a postal code is allocated in alphabetic sequence from east to west across Canada and denotes a province, territory or a major sector found entirely within the boundaries of a province. In Ontario, "K" denotes Eastern Ontario, "L" denotes Central Ontario, "M" denotes Toronto, "N" denotes Southwestern Ontario and "P" denotes Northern Ontario.

The first three characters of the postal code ("ANA") represent a set of well-defined and stable areas known as Forward Sortation Areas (FSAs). The FSA represents a specific area within a major geographical region or province. Rural FSAs are identifiable by the presence of a zero (0) in the second position of the FSA code. Often, rural postal codes represent the location of the place where the mail is sorted and not the final place of delivery.

Postal codes are included in many data sets, including hospital separations and mortality, live birth, and stillbirths since 1996, and are often used as an alternative means of geographic grouping by recoding using Statistic's Canada's Postal Code Conversion File (more details below). Postal code is often incomplete however, in many of the data sets.

The Office of the Registrar General (ORG) has its own geographic coding system. Data produced by the ORG goes to Statistics Canada prior to being distributed by the MOHLTC to public health units. For its own reports, Statistics Canada reassigns records to Census based geography based on the ORG code. The data file that MOHLTC receives has the Statistics Canada version of the ORG code and the postal code. Data that use this system include mortality, live births and stillbirths.

The Canadian Community Health Survey, cycles 1.1 and 2.1, includes data at two different levels in Ontario, the 37 Public Health Units and the 16 District Health Councils. This is the lowest level of geography available on the Public Use Microdata File and the Ontario sharing file. For special studies that require lower levels of geography special requests can be made to the MOHLTC. For the 1996/97 Ontario Health Survey there were 23 health areas, which were complete health units or groupings of health unit areas. The 1990 Ontario Health Survey included data at the level of the 42 Public Health Units and the 32 District Health Councils that existed at the time.

Conversion files are useful tools for integrating data from various sources. The Ministry of Health and Long Term Care produces conversion files that convert census sub-divisions to Ministry Residence Codes (county/municipality, Region, DHC, PHU) or postal codes to residence code and public health unit. The MOHLTC conversion files are updated annually to reflect changes to postal codes and to update the conversion between CSDs and residence codes. Because the residence codes reflect the municipal amalgamations, some of these areas are now too large for health planning purposes (i.e. Toronto). Also, some CSDs map to more than one Residence Code and some Residence Codes map to more that one CSD. The matching of one Residence Code for each CSD are therefore somewhat subjective and should not be considered "official".

Statistics Canada produces the Postal Code Conversion File (PCCF)³ which provides a correspondence between the six character postal code and Statistics Canada's standard geographical areas for which census data and other statistics are produced. The postal code conversion file contains multiple records for a postal code when the postal code straddles more than one block-face or dissemination area. Multiple records are quite common for rural postal codes and community mailboxes. The "single link indicator" was created to assist users in dealing with multiple records. The method used to establish the single link indicator attempts to identify the geographic area with the majority of dwellings using the particular postal code. Users should be cautioned that only a partial correspondence between the postal code and other geographic areas is achieved when using the single link indicator.

The PCCF is updated on a regular basis and is released every six months. The regular maintenance of the file takes the postal code changes continually introduced by Canada Post Corporation (CPC) and finds the corresponding census geographic areas. Every five years, after each census, the PCCF must be re-based to the new census geographic areas. The PCCF is a cumulative file and therefore includes both active and retired postal codes.

The MOHLTC subscribes to annual updates of the PCCF and uses the correspondence between the postal code and CSD to create the conversion files from postal code to Residence code and public health unit. Some postal codes do not respect municipal and county boundaries, especially in rural areas. This is a problem when using postal codes to assign county or health unit for an event.

Statistics Canada has also developed an application called PCCF+ that they make available to subscribers to the PCCF. The PCCF+ is a set of SAS programs and reference files that automatically assigns events to a full range of geographic areas, including health units, based on the postal code⁴. The PCCF+ system uses the most current PCCF file and the Weighted Conversion File (WCF) from the most recent census to distribute events across geographic areas that the postal code covers based on a population-based random allocation of cases among the possible areas. The PCCF and PCCF+ are available to health units from the MOHLTC, through its license with Statistics Canada.

References

1. Statistics Canada. 2001 Standard Geographical Classification. Volume I. The classification. Ottawa: Minister of Industry, 2002. . Available from: URL: http://www.statcan.ca/english/Subjects/Standard/sgc/2001/2001-sgc-index.htm
2. Statistics Canada. 2001 Census Dictionary. Ottawa: Minister of Industry, 2002. Available from: URL: http://www12.statcan.ca/english/census01/Products/Reference/dict/index.htm
3. Statistics Canada. Postal Code Conversion File, November 2001 Postal Codes, Reference Guide. Ottawa: Statistics Canada, 2002.
4. Russell Wilkins. PCCF+ Version 3F, User's Guide. Ottawa: Statistics Canada, January 2001
5. Statistics Canada. URL: http://www12.statcan.ca/english/census/index.cfm
6. Ontario Ministry of Health and Long-Term Care, Information Management. The Health Analyst's Toolkit, January 2006. URL: http://www.health.gov.on.ca/transformation/providers/information/im_resources.html