Differences in NHN Data

This section addresses known particularities, deviations or differences in NHN data as opposed to the initial National Hydro Network Standard. Since NHN data are produced using the best available source data - provincial data, for example - they de facto inherit from them. NHN data may, as a result, reflect source data limitations or constraints. In addition, all NHN data, produced via various NHN data production processes, inherit deviations introduced by the NHN Distribution Profile.

NHN Distribution Profile Deviations

NHN data available on the GeoBase Web portal according to the NHN Distribution Profile present some deviations (differences) compared with initial NHN Standard. These deviations are documented in the National Hydro Network, Distribution Profile Deviations, 2010-11-18 [pdf 49 KB].

For more information on the initial NHN Standard and on the NHN Distribution Profile, please refer to the National Hydro Network data Description / Documentation section, respectively under sub-sections NHN Standard (conceptual description) and NHN Product (data description).

Particularities in NHN data produced by Natural Resources Canada (NHN-CL4)

NHN data products produced by Natural Resources Canada (NHN-NRCan) following its initial NHN data production process (2007), namely NHN Completeness Level 4 (NHN-CL4) data, present the following particularities (in their Distribution Profile) compared with the initial NHN Standard:

  1. [Water Definition attribute] Attribute values "DITCH" (3), "TIDAL RIVER" (7) and "SIDE CHANNEL" (10) are not present in NHN data initially produced by Natural Resources Canada (NRCan).

Particularities in NHN-CL1 data produced by Natural Resources Canada

NHN data products produced by Natural Resources Canada (NHN-NRCan) following its NHN-CL1 data production process, namely NHN Completeness Level 1 (NHN-CL1) data; fully comply with NHN-CL1 minimal requirements. Read more on NHN Completeness Levels Main Characteristics.

NHN-CL1 data present the following particularities compared with the initial NHN Standard:

  1. [Littoral, Bank] NHN-CL1 data (Distribution Profile) do not contain the "Littoral" feature initially planned for in the NHN Hydro Network package. Actually, this feature has been replaced by the "Bank" feature for which the "WATER DEFINITION" attribute has the value "UNKNOWN" (-1).

  2. [Named Feature] NHN-CL1 data only contain point-type geometric representation "Named Feature" features. These features convey toponyms for which an automatic correspondence could not be established with a geometric feature from the Hydrographic Package.

  3. [Waterbody] NHN-CL1 data contains "Waterbody" entities located beyond the Canadian landmass where as the initial NHN Standard stipulates that they end at the coastline. The "WATER DEFINITION" attribute of such waterbodies then bears the value "UNKNOWN" (-1). This particularity results from the fact that at the Completeness Level 1, "WATER DEFINITION" attributes may be unknown. NHN-CL1 data progression to a higher level will establish "WATER DEFINITION" attributes for all "Waterbody" features and as a result, those located beyond the coastline will no longer be represented in the NHN.

  4. [Hydro Events package] According to the initial NHN data model, NHN events are created from the geometric intersection or geometric projection of a "Manmade Hydrographic Entity" or "Hydrographic Obstacle Entity" with a network linear element (Network Linear Flow or Bank). However, in NHN-CL1 data, all events found result from a geometric intersection only.

  5. [Entity Type attribute] The "Entity Type" attribute assigned to "Named Feature" entities from the Toponymic Package is always set to "Inland Water" (8) in the NHN. As a result, in NHN-CL1 data, it is possible that some "Named Features"" bearing this value may be located beyond the Canadian landmass as indicated above under [Waterbody]. As NHN-CL1 data progress to a superior completeness level, such "Named Features" will no longer be part of the NHN.

  6. [Flow Direction attribute] In NHN-CL1 data, only "Network Linear Flow" features having the value "PRIMARY" (1) for the "Level Priority" attribute and the value "FALSE" (0) for the "Isolated" attribute are oriented (digitizing direction) downstream. They therefore bear the value "Same Direction" (1) for the "Flow Direction" attribute. All other "Network Linear Flow" features either bear the value "UNKNOWN" (-1) or "N/A" (3) for their "Flow Direction" attribute.

  7. [Level Priority attribute] In NHN-CL1 data, the "PRIMARY" value for the "Level Priority" attribute which qualifies the main Network Linear Flow path within a hydro network is allocated based on the shortest path principle instead of the size and importance of the watercourse. Thus, in NHN-CL1 data, it is possible to have a narrow and shallow section of a watercourse be identified as "PRIMARY ", whereas a wider, deeper and longer alternate section is identified as "SECONDARY".

Particularities in NHN-CL2 data produced by Natural Resources Canada

NHN data products produced by Natural Resources Canada (NHN-NRCan) following its NHN-CL2 data production process, namely NHN Completeness Level 2 (NHN-CL2) data; fully comply with NHN-CL2 minimal requirements. Read more on NHN Completeness Levels Main Characteristics.

NHN-CL2 data present the following particularities compared with the initial NHN Standard:

  1. [Named Feature] NHN-CL2 data only contain point-type geometric representation "Named Feature" features. These features convey toponyms for which an automatic correspondence could not be established with a geometric feature from the Hydrographic Package.

  2. [Hydro Events package] According to the initial NHN data model, NHN events are created from the geometric intersection or geometric projection of a "Manmade Hydrographic Entity" or "Hydrographic Obstacle Entity" with a network linear element (Network Linear Flow or Bank). However, in NHN-CL2 data, all events found result from a geometric intersection only.

  3. [Flow Direction attribute] In NHN-CL2 data, only "Network Linear Flow" features having the value "PRIMARY" (1) for the "Level Priority" attribute and the value "FALSE" (0) for the "Isolated" attribute are oriented (digitizing direction) downstream. They therefore bear the value "Same Direction" (1) for the "Flow Direction" attribute. All other "Network Linear Flow" features either bear the value "UNKNOWN" (-1) or "N/A" (3) for their "Flow Direction" attribute.

  4. [Level Priority attribute] In NHN-CL2 data, the "PRIMARY" value for the "Level Priority" attribute which qualifies the main Network Linear Flow path within a hydro network is allocated based on the shortest path principle instead of the size and importance of the watercourse. Thus, in NHN-CL2 data, it is possible to have a narrow and shallow section of a watercourse be identified as "PRIMARY", whereas a wider, deeper and longer alternate section is identified as "SECONDARY".

Deviations in NHN-CL4 Data from British Colombia

British Colombia NHN Data (NHN-BC) present the following deviations compared with the initial NHN Standard:

  1. [Manmade Features] The BC-NHN does not contain Lock Gate, Boat Ramp, or Fish Ladder manmade features.

  2. [Obstacles] The BC-NHN does not contain Reef, Rocks, Exposed Shipwreck or Ford features obstacle features.

  3. [Network Linear Flow] The BC-CWB dataset contains culverts, storm sewers, and other inferred edges used for stream connectivity. These features are not observed and will not be present in the NHN Hydrographic package, however these edges are present in the NHN Network Linear Flow Class with a Network Flow Type of Constructed.

  4. [Obstacles and Manmade Features] The BC-NHN contains dam, falls, dock and wharf features which may exist as "Points" or "Lines" inside of a waterbody. They may also exist on isolated single line watercourse features.

  5. [Toponymy] In BC-CWB the toponymic information of named streams is only captured on the stream network. However in NHN this information is captured on both the network and hydrographic packages. Because of the constructed features in the CWB dataset there is a many-to-many relationship between the network linear flow and single line watercourse features. This many-to-many relationship results in single line watercourse features that are comprised of multiple network linear flow features of which only parts may be named. In BC-NHN, however, the entire single line watercourse feature is named which results in toponymic inconsistencies. For accurate toponymic information, the network linear flow named features should be used.

  6. The BC international or provincial/territorial boundary does not match the GeoBase geopolitical boundaries along the BC-Alaska and BC-Washington, BC-Idaho, BC-Montana or BC-Alberta borders. The differences vary on either side by up to 2 km with the largest differences occurring along the BC-Alaska and BC-Alberta Borders

  7. [Manmade Features] The mapping of BC DryDock, FerryDock, MarinaDock, Pier/Wharf to NHN manmade features is as follows:

    • BC DryDock = NHN Slip
    • BC FerryDock = NHN Wharf
    • BC Marina Dock = NHN Wharf
    • BC Pier/Wharf = NHN Wharf

  8. [Manmade Features: Wharf] The wharf manmade features were generated with the following additional spatial constraints: wharf CROSSES littoral OR relate (wharf, waterbody, FTT******).

  9. [Events] The BC-NHN contains only events for manmade and obstacle features that are projected less than or equal to 10 metres.

    BC manmade events for non-dike entities were generated by:

    1. Creating events for intersections between manmade entities and associated network linear features:

      • A linear event was created for each network linear feature from the two further intersection points along the feature.
      • A point event was created if only a single intersection existed for the network linear feature (note that multiple point events will occur at the same x,y location if the entity intersects the network linear feature at a node (junction)).

    2. Creating projected events for remaining entities.

      • For point entities, point events were created by using the nearest point along a network linear element within 10m.
      • For linear entities, the entities were intersected with all network linear features buffered by 10m. For each resulting intersecting feature, the start and end point of the geometry were projected back to the network linear feature and a linear event was created using the two point furthest away from each other on the network linear features. If the resulting linear event was less than 5m it was converted to point event (in an attempt to meet the requirement that entities that are perpendicular to network linear features create point events).
      • For polygonal entities, point events were created on the nearest network linear element within 10m of the polygon entity.
      • For all features if line events were created, point events were not created.
      • Dike events were generated using an intersection between 100m buffer around the dike and all associated network linear features within 100m. Next, cases where the entire network linear feature associated with the event was greater than 10m away from the dike entity were removed. This implies that a dike entity may have multiple events along multiple banks or littorals and dike events may be created along the network linear feature where part of the feature is greater than 10m from the dike entity; however, some other part of the feature must be within 10m. The reason for doing this was that there are many dikes that move in and out of the 10m range which would have resulted in many tiny linear events which is not representative of the data.

    BC obstacles events were generated by:

    1. Creating events for intersections between obstacle entities and associated network linear features:

      • For linear intersections 2-vertex linear events were created.
      • For point intersections point events were created.

    2. Projected events were created for all entities without intersecting events and whose network linear element lies within 10m of the obstacle entity.

      • For point, line, and polygon entities, point events were created by using the nearest point along a network linear element within 10m

  10. [Manmade features] The BC-NHN contains one Dam feature which is associated with an isolated Single line watercourse.

  11. [Obstacles] The BC-NHN contains 11 Falls features that are associated with an isolated Single line watercourse.

  12. [Toponymy] The BC-NHN has not attached river names to lake features as per the NHN model.

  13. Along the BC / USA borders, BC has used extra-jurisdictional data when computing isolated attributes. Thus, some features along the border may be flagged as not isolated because data exists in the extra-jurisdictional regions.

The TRIM data product (which was used as input to the BC-NHN) contains the following specifications:

  1. The TRIM dataset was captured from stereoscopic photo interpretation with a horizontal planimetric accuracy of +/- 10m, 90% of the time, and a vertical accuracy of +/- 10m, 90% of the time.
  2. Any hydrographic feature is captured as linear when the feature is less than 20m wide, and polygonal when greater.
  3. The minimum size of a lake is captured where the longest dimension is over 25 meters.
  4. The maximum stream width at which the feature is captured as a line is 20 meters or less.
  5. The maximum width at which the canal is captured as a line is 20 meters or less.
  6. The coastline definition is captured at the high tide mark (high water level).
  7. The maximum width at which a dock or wharf is captured as a line is 20 meters or less.

Particularities in NHN Data from Ontario (NHN-CL2)

NHN data created from Ontario provincial data (NHN-ON) were produced via the NHN-Hybrid model. This model which is a simplified version of the NHN model is used as an intermediate model to facilitate the creation of NHN data from provincial data. Read more on the NHN-Hybrid model in the NHN Implementation Strateg

NHN data produced following the NHN-ON production process fully comply with the NHN-CL2 minimal requirements. This data however presents some particularities compared with initial NHN Standard. These particularities either result from the content or data structure of the Ontario NHN-Hybrid data, or from final NHN data creation by Natural Resources Canada (NRCan).

  1. [Network Linear Flow] The NHN-ON does not present "Network Linear Flow" features within headwater waterbodies, within some waterbodies with no outlet, nor in isolated waterbodies or waterbodies at the extremity of isolated networks. Also, a limited number of "Inferred/Secondary" types "Network Linear Flows" are present around islands. Such "Network Linear Flows" are only present when islands meet specified criteria established by the Land Information Ontario (LIO) division of the Ontario Ministry of Natural Resources (OMNR), which are described in the "Data Capture Specification for Hydrographic Features" document. All NHN-ON "Network Linear Flows" are however oriented, meaning that they all have the value "Same Direction" (1) for the "Flow Direction" attribute. These particularities result from Ontario NHN-Hybrid data content and structure.

  2. [Hydro Events package] According to the initial NHN data model, NHN events are created from the geometric intersection or geometric projection of a "Manmade Hydrographic Entity" or "Hydrographic Obstacle Entity" with a network linear element (Network Linear Flow or Bank). However, in NHN-ON data, all events found result from a geometric intersection only. This particularity results from final NHN data creation by NRCan.

  3. [Toponymic Information] Toponymic Information provided by the OMNR may be partial, which is why 2 toponymic data sources were used in the NHN-ON data creation; first geographical names from OMNR Geographic Named Extent Layer (GEL) files from the Ontario Geographic Names Data Base and those from the Canadian Geographical Names Data Base.

    The official toponymy of Ontario as authorized through the Ontario Geographic Names Board Act can be obtained from the Ontario Geographic Named Extent Layer which is available through the Land Information Ontario (LIO) warehouse.

  4. [Hydrographic Obstacle Entity: Dam] The NHN-ON presents "Hydrographic Obstacle Entities: Dam" sometimes positioned outside of waterbodies or not on single line watercourse features. Some Dams may be found within Lake type waterbodies. It is also possible that some Dams may not be position on a Network Linear Flow network even if adjacent to a waterbody. These particularities result from Ontario NHN-Hybrid data content.

Particularities in NHN Data located on the United-States territory

NHN data located on the United-States territory were created using NHD high resolution data (National Hydrography Dataset from USGS). Once aligned to Canadian NHN data, they were correlated to the NHN-Hybrid production model (simplified version of the NHN model), then they were used in the creation of trans-boundary Canada/USA NHN data. Read more on the NHN-Hybrid model in the NHN Implementation Strategy.

NHN data located on the American territory present some particularities compared with initial NHN Standard. These particularities either result from the NHD content or structure or from final NHN data creation by Natural Resources Canada (NRCan).

  1. [NHN Completeness Level] The NHN Completeness Level definition does not apply to the American portion of NHN trans-boundary Canada/USA NHN Work Units as the NHN Completeness Level Approach is designed to allow a progressive creation of the NHN in Canada only, thus the Completeness Level was not established for the American portion of the data. Read more on the NHN Completeness Levels.

  2. [Network Linear Flow] NHN data located on the American territory does not present "Network Linear Flow" features within headwater waterbodies nor within isolated waterbodies. Also, no "Network Linear Flows: Secondary" are present around islands; only "Network Linear Flows: Primary" are represented within waterbodies. These particularities result from NHD data content.

  3. [Hydro Events package] According to the initial NHN data model, NHN events are created from the geometric intersection or geometric projection of a "Manmade Hydrographic Entity" or "Hydrographic Obstacle Entity" with a network linear element (Network Linear Flow or Bank). However, in NHN data produced via the NHN-trans-boundary process, all events found result from a geometric intersection only. This particularity results from final NHN data creation by NRCan.

  4. [Toponymy Package] NHN data located on the American territory does not present any "Named Feature" features except for a few area type ones originating from named "NHD Area Bay/Inlet" polygons features. This particularities result from NHD data content.

  5. [Toponymic Information] "Island" and "Waterbody: Watercourse" entities do not bear names in NHN data located on the American territory. This particularities result from NHD data content.

  6. [Data Structure] NHN data structure of features located on the U.S. territory was not subject to a detailed spatial constraint validation; the objective being to mainly ensure the continuity of the hydro network on both sides of the international boundary. NHD data thus was correlated to the NHN model without modifying excessively its data structure.