Wednesday, November 3, 2004

Enumeration Areas and Dissemination Areas


Is an EA typically larger than a DA, or smaller - or is it impossible to generalize? I'm trying to get a sense of the comparative size of these two units. (From browsing the concordance between EAs and DAs, I get a sense that quite a few DAs fit into or overlap an EA, but I'd rather be sure)


DAs were brought in to replace EAs, so some are the same size, some are bigger, and some are smaller. Here is the explanation about them.

The dissemination area (DA) is a new standard geographic area. It replaces the enumeration area (EA) as a basic unit for dissemination. Dissemination areas are aggregates of one or more blocks. DAs respect several delineation criteria designed to maximize their usefulness for data analyses.

1. 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.

2. DAs 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.

3. DA 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.

4. A DA within a DA is formed when the population of apartment or townhouse complexes meets or exceeds 300 persons.

5. DAs are compact in shape, to the extent possible while respecting the above criteria.

6. Operational requirements limit to 99 the number of blocks that can be included in a DA. In order to meet the operational constraint of releasing population and dwelling counts in the spring following the census year, the population counts used to delineate DAs are taken from the previous census. To delineate DAs for 2001, sufficiently accurate block population counts based on 1996 Census data were only possible where block-face geocoding existed for the 1996 Census. Therefore, the 2001 DAs were delineated according to the above criteria only in CMA/CA areas where 1996 block-face geocoding existed. Everywhere else, the 2001 DAs are the same as the 2001 EAs used for data collection.

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