Dissemination area: Detailed definition
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A dissemination area (DA) is a small, relatively stable geographic unit composed of one or more adjacent dissemination blocks. It is the smallest standard geographic area for which all census data are disseminated. DAs cover all the territory of Canada.
2011, 2006, 2001
For 2011, dissemination areas (DAs) were defined as needed, rather than being completely re-delineated. This was to help ensure the comparability of data since the previous census. To do this, planners located in areas with census tracts were surveyed for their input regarding the delineation of DAs that experienced high population growth between the 2001 and 2006 Censuses or that exceeded the DA maximum population limit. Other user-defined DA updates were accepted in areas where the DA structure either changed substantially between 2001 and 2006 as a result of automated delineation or simply did not provide users (local area experts) with relevant data since the DAs were not representative of their communities. The implementation of both of these types of user-defined updates eliminated the requirement for a fully automated delineation, which was used in previous censuses.
Dissemination area rules
Dissemination areas respect several delineation criteria designed to maximize their usefulness for data analysis and to meet operational constraints.
- Dissemination area (DA) boundaries respect the boundaries of census subdivisions and census tracts. DAs therefore remain stable over time, to the extent that census subdivisions and census tracts do.
- Dissemination area boundaries follow roads. DA boundaries may follow other features (such as railways, water features, power transmission lines), where these features form part of the boundaries of census subdivisions or census tracts.
- Dissemination areas are uniform in terms of population size, which is targeted from 400 to 700 persons to avoid data suppression. DAs with lower population counts (including zero population) may result in order to respect the boundaries of census subdivisions and census tracts. DAs with higher population counts may also result.
- Dissemination areas are delineated based on the block population counts from the previous census due to operational constraints.
- Dissemination areas are compact in shape, to the extent possible while respecting the above criteria.
- The number of dissemination blocks that are included in a dissemination area is limited to 99 due to operational constraints.
Dissemination area codes
Each dissemination area (DA) is assigned a four-digit code. In order to uniquely identify each DA in Canada, the two-digit province/territory (PR) code and the two-digit census division (CD) code must precede the DA code. For example:
|12 09 0103
|59 09 0103
When dissemination areas were first created, geographic proximity was embedded in the DA code by assigning DA codes in a serpentine manner within each census division. As DAs evolve, this coding structure cannot be maintained. Therefore, DA codes can no longer ensure geographic proximity.
Table 1 in the Introduction shows the number of dissemination areas by province and territory.
Changes prior to the current Census
In 2006, dissemination areas (DAs) were delineated outside of census metropolitan areas (CMAs) and census agglomerations (CAs) using an automated area delineation system. Within CMAs and CAs that contained census tracts (CTs), DAs were kept relatively stable since the previous census. Some DAs in these areas were adjusted to respect changes to CT, CA, and CMA boundaries.
In 2001, the DA was a new standard geographic area. It replaced the enumeration area (EA) as a basic unit for dissemination. The 1996 population counts were used to delineate the DAs, mainly in block-face geocoding areas of CMAs and those CAs that contained CTs. Everywhere else, the 2001 DAs were the same as the 2001 EAs used for data collection.