# Terms and Definitions

This document provides a standardized lexicon for the **Data for Canada (D4C)** project, categorized by data package and infrastructure component.

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## 1. Foundation Data Package

Terms related to base-layer datasets and structural identifiers.

* **[DGUID (Dissemination Geography Unique Identifier)](https://www12.statcan.gc.ca/census-recensement/2021/ref/dict/az/Definition-eng.cfm?ID=geo055):** An alphanumeric code used by Statistics Canada to uniquely identify a geographic area. It incorporates the vintage (year), type, and specific area code.
* **[Building Footprint](https://www.dataforcanada.org/docs/d4c-pkgs/d4c-datapkg-foundation/):** The two-dimensional boundary of a building’s ground-level perimeter, primarily sourced from the Open Database of Buildings (ODB).
* **[Cloud-Native Geospatial](https://www.dataforcanada.org/docs/getting_started/):** Data formats (e.g., Parquet, GeoZarr) optimized for cloud storage and efficient partial-file reading over HTTP.
-->

## 1. Statistical Data Package

Standard geographic areas from the 2021 Census of Population hierarchy, as defined by Statistics Canada.

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  These concepts are key to working with Statistical and Census data from Statistics Canada.
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* **[DGUID (Dissemination Geography Unique Identifier)](https://www12.statcan.gc.ca/census-recensement/2021/ref/dict/az/Definition-eng.cfm?ID=geo055):** An alphanumeric code used by Statistics Canada to uniquely identify a geographic area. It incorporates the vintage (year), type, and specific area code.

![geographic hierarchy](geographic-hiearchy.webp)

### Administrative Areas

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* **Canada:** The highest level of geography, covering the entire country.
* **[Province or Territory (PR)](https://www150.statcan.gc.ca/n1/pub/92-195-x/2021001/geo/prov/prov-eng.htm):** The primary political-administrative subdivisions of Canada.
* **[Census Division (CD)](https://www150.statcan.gc.ca/n1/pub/92-195-x/2021001/geo/cd-dr/cd-dr-eng.htm):** A group of neighboring municipalities joined together for the purposes of regional planning and managing common services.
* **[Census Subdivision (CSD)](https://www150.statcan.gc.ca/n1/pub/92-195-x/2021001/geo/csd-sdr/csd-sdr-eng.htm):** The general term for municipalities or areas treated as municipal equivalents for statistical purposes.
* **[Federal Electoral District (FED)](https://www150.statcan.gc.ca/n1/pub/92-195-x/2021001/geo/fed-cef/fed-cef-eng.htm):** An area represented by a Member of Parliament in the House of Commons.
<!-- TODO: Geographic regions of Canada (GRC). StatCan does not technically provide boundaries, had to create them myself. Add definition, maybe a link to where people can send their feedback on not having official GRC boundaries-->

### Statistical Areas

* **[Aggregate Dissemination Area (ADA)](https://www150.statcan.gc.ca/n1/pub/92-195-x/2021001/geo/ada/ada-eng.htm):** A dissemination geography created by grouping existing dissemination areas, census subdivisions, or census tracts to achieve a target population.
* **[Census Metropolitan Area (CMA)](https://www150.statcan.gc.ca/n1/pub/92-195-x/2021001/geo/cma-rmr/cma-rmr-eng.htm):** An area consisting of one or more adjacent municipalities situated around a major urban core with a total population of at least 100,000.
* **[Census Agglomeration (CA)](https://www150.statcan.gc.ca/n1/pub/92-195-x/2021001/geo/cma-rmr/cma-rmr-eng.htm):** Similar to a CMA, but with a core population of at least 10,000.
* **[Census Tract (CT)](https://www12.statcan.gc.ca/census-recensement/2021/ref/dict/az/Definition-eng.cfm?ID=geo013):** Small, relatively stable geographic areas within CMAs and CAs that usually have a population between 2,500 and 8,000.
* **[Dissemination Area (DA)](https://www12.statcan.gc.ca/census-recensement/2021/ref/dict/az/Definition-eng.cfm?ID=geo021):** A small, stable geographic unit composed of one or more adjacent dissemination blocks.
* **[Dissemination Block (DB)](https://www12.statcan.gc.ca/census-recensement/2021/ref/dict/az/Definition-eng.cfm?ID=geo022):** An area bounded on all sides by roads and/or boundaries of standard geographic areas; the smallest unit of census geography.
* **[Economic Region (ER)](https://www12.statcan.gc.ca/census-recensement/2021/ref/dict/az/Definition-eng.cfm%3FID%3Dgeo023):** A grouping of complete census divisions created as a standard geographic unit for analysis of regional economic activity.
* **[Population Centre (POPCTR)](https://www12.statcan.gc.ca/census-recensement/2021/ref/dict/az/Definition-eng.cfm?ID=geo049a):** An area with a population of at least 1,000 and a density of 400 or more people per square kilometer.
<!-- Gemini can sometimes be...unsmart>
<!--* **[Rural Area](https://www12.statcan.gc.ca/census-recensement/2021/ref/dict/az/Definition-eng.cfm?ID=geo042):** All territory lying outside population centres.-->

## 3. Orthoimagery & Field Imagery Packages

Terms related to imagery processing and remote sensing.

* **[Orthoimagery](https://www.dataforcanada.org/docs/d4c-pkgs/d4c-datapkg-orthoimagery/):** Aerial or satellite imagery geometrically corrected ("orthorectified") such that the scale is uniform, allowing for accurate measurements of distance.
* **[Photogrammetry](https://www.dataforcanada.org/docs/d4c-pkgs/d4c-datapkg-field-imagery/):** The science of making measurements from photographs, used to generate 3D models and orthomosaics.

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## 4. Infrastructure & Distribution

Terms related to the decentralized delivery of D4C data.

* **[Source Cooperative](https://www.dataforcanada.org/infrastructure/):** A cloud-native data publishing utility where D4C hosts primary repositories.
* **[SpatioTemporal Asset Catalogs (STAC)](https://www.dataforcanada.org/docs/d4c-infra-distribution/):** A specification that provides a common language to describe geospatial datasets so they can more easily be indexed and discovered.
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