IMRC - Geographic Coverage Sub-group: Usage Guidelines

Coverage

Introduction

The Coverage element is used to spatially reference  Government of Canada Web resources, using descriptors from controlled vocabularies, authority files, or using a spatial reference system like geographic coordinates. The Dublin Core Metadata Initiative (DCMI) endorses element refinements that state whether spatial or temporal extent is being expressed. This document provides guidance for spatial coverage only.

The use of the Coverage element is optional.

Why Use Coverage?

Coverage is used when there is a distinct and definable spatial extent to the resource and there is a business requirement to enable the identification of the resource by its unique geographic location. When Coverage is implemented,  the spatial information contained within the element can be used to perform powerful searches that allow a user to search on a specific location, exclude certain areas, sort by nearest location, and many other operations.

When to Use Coverage

The following examples illustrate appropriate usage of the coverage element:

Example 1:
Web resources that contain information on employment opportunities for various regions  contains information that is organized by area. The Coverage element will contain a geographic descriptor, geocode or spatial coordinates that define the areas referenced by the resource. This could enable a user to search on employment opportunities for a specific area.

Example 2:
Web resources that identify national historical sites contain information that specifies a geographic location. The Coverage element will contain a geographic descriptor, such as a place name, postal code or spatial coordinates that define the location of the site(s). This could enable a user to search for historical sites within a certain radius, or along a route of travel.

When NOT to Use Coverage

Coverage should not be used if there is not a distinct and definable geographic extent to the resource or there is no business requirement to utlilize the unique spatial reference(s) specifically or inherently contained in the resource contents .  For instance,  use of the term "Canada" to describe federal government online resources that are "Canadian" but not directly relatable to the geographic boundaries of Canada is not recommended.

How to Use Coverage

Coverage must be populated using a controlled vocabulary, authority file or other registered scheme. Controlled vocabularies or authority files recommended by these guidelines for usage with Coverage are registered with Library and Archives Canada (LAC) and can be accessed at http://www.collectionscanada.ca/8/4/r4-280-e.html. As well, all recommended schemas are able to be translated to unique geographic location, expressed as spatial coordinates. Named geographies from known, controlled sources can be translated to simple geographic coordinates (a point) or more complex geometries (bounding box, polygons or lines) via web services, such as the CGDI Gazetteer Service (http://cgdi-dev.geoconnections.org/prototypes/cgdigaz/index.htm).

Departments are strongly encouraged to register other standardized geographic  descriptors, geocodes or other resource, which may better meet their particular requirements, with LAC.  They are registered under a unique scheme name that must be stated in every instance of Coverage.

The most appropriate choice of vocabulary depends on the resource being documented. More than one vocabulary may be used to describe a single resource. Repeat the Coverage element as needed, using the appropriate scheme name each time, for every location described in the resource.

Guidelines for Encoding Schemes Currently Registered for use with Coverage by LAC

Please note that all examples provided below are in HTML.

Canadian Geographical Names Data Base (CGNDB)
http://geonames.nrcan.gc.ca/index_e.php
This database contains the official names of Canada's provinces and territories; names of cities (an inhabited place, a town, village, etc.); topographical features, conservations areas, military areas and Indian reserves. The CGNDB provides the latitude and longitude coordinates for a point representing the approximate geographic location.

Place names are rarely unique. Place names must be supplied at a sufficient granularity to unambiguously identify the location. To format, start with the largest geographical unit and end with the smallest, plus the CGNDB concise code (i.e. country; province/territory; municipality, concise code). For a topographical feature, format as country; province/territory; administrative/geographical locality; feature name; concise code. Separate descriptors with a semi-colon. Semi-colons must be used since values in the CGNDB may contain commas. Repeat the Coverage element for each location.

Using this encoding scheme, the metadata for a resource containing employment opportunity information, <dc.coverage.spatial> would read:

   <meta name="dc.coverage.spatial" scheme="gcgeonames"
     content="Canada; Ontario; Peterborough; Unincorporated Area">

Regions of Canada
http://geodiscover.cgdi.ca/gdp/util/etc/CanadaProvRegions.jsp
This vocabulary consists of Canada's provinces and territories, six large inter-provincial regions and 39 intra-provincial regions. The list provides names for commonly recognized areas within Canada. The boundaries are based upon census divisions or provincial and territorial boundaries, and therefore have an associated geometry. Repeat the element for each location.

Using this encoding scheme, Coverage for a resource containing agricultural output statistics for Canadian prairie farms would read:

   <meta name="dc.coverage.spatial" scheme="gcregions"
     content="Canada; Canadian Regions;Prairie Provinces">

Getty Thesaurus of Geographic Names (TGN)
http://www.getty.edu/research/conducting_research/vocabularies/
The TGN can be used as a source for international (non-Canadian) place names. It is preferred by the DCMI as a source for international place names. The TGN provides the latitude and longitude coordinates for a point representing the approximate geographic location.

Place names are rarely unique. Place names must be supplied at a sufficient granularity to unambiguously identify the location. To format, start with the largest geographical unit and end with the smallest (i.e. country; province/territory; municipality). Separate descriptors with a semi-colon. Semi-colons must be used since values in the TGN database may contain commas. Repeat the element for each location.

Using this encoding scheme, Coverage for a resource involving plans for a war memorial in Southeastern England would read:

   <meta name="dc.coverage.spatial" scheme="tgn"
     content="United Kingdom; England; Devon; Exeter">

ISO 3166 – Country Codes
http://www.iso.ch/iso/en/prods-services/iso3166ma/02iso-3166-code-lists/list-en1.html
ISO 3166 can be used as a source to identify international (non-Canadian) country names. This authority list is registered with the DCMI as a source for country names. Note that as a best practice, complete place names should be used in preference to abbreviations or symbols. Repeat the element for each location.

Using this encoding scheme, Coverage for a resource on the spread of SARS in Southeast Asia (China, the Philippines and Singapore) would read:

   <meta name="dc.coverage.spatial" scheme="ISO 3166" content="CN">
   <meta name="dc.coverage.spatial" scheme="ISO 3166" content="PH">
   <meta name="dc.coverage.spatial" scheme="ISO 3166" content="SG">

Canadian Postal Codes
http://www.canadapost.ca/splash.asp
A postal code is a descriptor representing a section of a street, a collection of streets, an establishment, a structure, a group of post office boxes, and so forth. Using tools such as the Canada Postal web lookup service, postal codes can provide the latitude and longitude coordinates for a point representing the approximate geographic location (centroid) of the postal code. Repeat the element for each location.

Example:

   <meta name="dc.coverage.spatial" scheme="gcpostal" content="K0A3P0">
   <meta name="dc.coverage.spatial" scheme="gcpostal" content="K1A0E9">

DCMI Point
http://www.dublincore.org/documents/dcmi-point/
DCMI Point is a scheme for uniquely identifying a point on the Earth's surface using its geographic coordinates. Repeat the element for each point in space referred to in the resource described. Please refer to the DCMI guidance for further details on how to use this scheme.

Example for Grand Valley, Ontario, Canada would read:

   <meta name="dc.coverage.spatial" scheme="DCMIPoint"
     content="north=43.9;east=-80.31>

DCMI Bounding Box
http://www.dublincore.org/documents/dcmi-box/
DCMI Bounding Box is a scheme for uniquely identifying an area on the Earth's surface by defining its geographic limits as a bounding box. Repeat the element for each area referred to in the resource being described. Please refer to the DCMI guidance for further details on how to use this scheme.

Example for Prince Edward Island, Canada would read:

   <meta name="dc.coverage.spatial" scheme="DCMIBox"
     content="northlimit=47.0; southlimit=-45.9; westlimit=-64.5;
     eastlimit=-62.0">