Many government mapping agencies promote their geospatial data as authoritative or as created from authoritative sources. Many people use the term "authoritative geospatial data," but what does it really mean?
Authoritative is a term that one often sees or hears when someone is describing geospatial data. If one searches the federal open data portal at data.gc.ca for the word “authoritative” it returns “2,248 datasets found for authoritative." Even the vision of the Canadian Geospatial Data Infrastructure (CGDI) contains the word authoritative - “CGDI Vision: To enable access to the authoritative and comprehensive sources of Canadian geospatial information to support decision-making.”
The word "authoritative" makes it sound impressive, but what does it really mean?
Land surveyors were probably the first to use the term authoritative geospatial data and they have been producing authoritative data for some time. Surveyors define authoritative as data that contains a surveyor’s professional stamp and that the data can be used for engineering design, determination of property boundaries and permit applications. In essence, the term carries a certification of positional accuracy.
The Pan-Canadian Action Plan for GeoBase II and Collaborative Geospatial Architecture Working Group Final Report indicated the following:
- The term “authoritative” should be applied only to data that is legislated or regulated;
- Should it be necessary to differentiate data supplied by government agencies from other sources of data – it is suggested that discussion should be about “trusted” data; and
- Validation must be part of the certification of authoritativeness.
For many GIS practitioners, the term usually means that the data was produced or is approved by some authority. Esri Canada aggregates various authoritative data for the production of the Community Map of Canada.
Figure 1.1: The Canadian Community Map from Esri Canada contains a significant amount of authoritative data
So there are lots of definitions, but the current general understanding is that authoritative geospatial data comes from some government source. But does authoritative data mean that the data is complete, current and accurate?
Today, many levels of government are being encouraged to release their data for others to access and reuse through enlightened open data policies. Across Canada, open authoritative data portals are being developed for social and economic spinoff benefits. Authoritative data releases are a global phenomenon and even the G8 countries got involved by signing the G8 Open Data Charter. This is a promising and noble undertaking by these governments to make authoritative data available for further external uses.
So if you download authoritative geospatial data, does it contain all the layers and all the features in your area of interest or just the ones that the government needed? Often governments do additional checks on the data, which slows down data release cycles, thus the currency of the data may be in question. More generally, is the data fit for your use in terms of both geometric and attribute accuracy?
GIS practitioners should make sure they “check it out” before using authoritative data to ensure that the data meets the quality, currency and accuracy requirements of their application.