NHN Implementation Strategy

After the NHN Standard was nationally adopted in August 2004, the team from the Centre for Topographic Information Sherbrooke (CTIS) was given the mandate to implement the NHN. The latter is implemented under the leadership of the National Hydro Network Project from the Earth Sciences Sector Contribution to GeoBase Program, Natural Resources Canada (NRCan). Discussions to produce NHN data in partnership were then engaged with some provincial/territorial partners. Agreements were then concluded with British Columbia, Manitoba and Yukon.

The agreement with British Columbia was assigning the responsability of the NHN data production to the province, whereas those with Manitoba and Yukon gave this responsibility to CTIS. While British Columbia was developing its own NHN data production process based on using provincial source data, an initial production process was also developed and used by CTIS to produce NHN data in about 40 drainage areas or NHN Work Units (WU) elsewhere in the country, of which 28 in northern Manitoba and 6 in the Yukon. It was realized during this initial production that it was difficult to process (assemble or update) all NHN data at once. The most important problems noted were the large volume of features per WU, numerous references to other features (via identifiers), and the presentation of the same information/geometry in different features (e.g. banks vs waterbodies, obstacle features vs obstacle events).

Moreover, the emergence of new constraints required a review of the initial NHN Implementation Strategy, which led to the development of a new NHN Implementation Strategy based on the following elements:

  • Availability of new SPOT imagery as a source for updating;
  • Need for a simplified model to facilitate data updates and the implication of partners;
  • Creation of NHN data by stages (completeness levels);
  • Quick implementation of a first NHN national coverage.

The Medium Resolution Imagery (MRI/GeoBase) project launched in 2005 with the goal of covering the entire country in a five-year period (2005-2010) with cloud free SPOT orthoimages (with a 10-metre resolution for the panchromatic band and 20-metre for multispectral bands), and the implementation of a simplified NHN model, called NHN-Hybrid, used as an intermediate model in the production of NHN data, enables meeting the NHN need for data updates.

In order to quickly provide users with NHN data, an implementation-by-stage approach, developed in consultation with provincial and territorial partners across the country and called Completeness Level (CL) Approach, was developed. In this new approach, levels are defined and completed in successive production phases, thus making intermediary results available to users. According to this approach, each WU has its own specific completeness level. Each level is backward compatible regarding data content. This implies that a superior level contains all of the data content from a lower level and more. Thus, in regards to content, a lower level is always a subset of a superior one.

With this approach, users get a clear description of the completeness level status for each WU. Four Completeness Levels (CL1 to CL4) were defined under this approach. The new NHN Implementation Strategy progressively allows reaching the required content and structure of the NHN. The NHN Completeness Levels section describes the characteristics of the four NHN completeness levels distributed on GeoBase.

It is thus in early 2008 that re-started the NHN data production. The CTIS then implemented an automatic NHN data production process using NRCan's digital topographic data. This process enables, depending on the source data content, reaching either the NHN Completeness Level 1 or 2 for each WU. This is how the initial NHN data production in Manitoba and the Yukon was completed. This same process is also used to create the first national NHN data coverage, where thus far more than 95 % of the Canadian territory is now available.

Since the application of the new NHN Implementation Strategy, 2 new partnership agreements have been concluded with the provinces of Ontario and Quebec. These provinces may then produce their NHN data according to the NHN completeness Level permitted by the content and data structure of their provincial data. They may also opt to produce their data in accordance with the NHN model or the NHN-Hybrid production model.