Horizontal: Because this is a '4th generation' derived dataset ('4th Generation' meaning the Derivation Process: 1) Original data based on OBM DTM and/or contours ---> 2) Interpolated to created a DEM ---> 3) Further interpolated to create Enhanced Flow Directions ---> 4) Final Watershed Creation), the level of accuracy declines with each derivation especially in flat or uncontrolled terrain. Therefore, the following statements of accuracy should only be used as a guide. Where the terrain is well defined (eg. hilly terrain), actual accuracy may exceed the stated accuracies. Southern Ontario: +/- 100 m Near North (up to 50 Degree Latitude): +/- 400 m ; Vertical: Not Applicable
Enhanced Flow Direction grid (EFDIR, EFD, EFDG): NRVIS-based enhanced flow direction grid version 2.1.0/2.1.1 (derived from the Provincial DEMv2). DEM related data collected from OBM and CA information ranging from 01/01/1976 to 31/12/2008. EFD Data collected from 01/01/2004 to 31/12/2008. The enhanced flow direction grid is a derivative from the Provincial DEM, regular Flow Direction grid, water flow and water polygons. Each cell in this grid represents the direction of flow, which is determined by finding the direction of steepest descent from each cell. The flow directions have been 'enhanced' such that the hydrology on the known network is honoured 100 percent with the exception of some shared headwater wetlands and lakes. Where these shared waterbodies exist, the underlying DEM elevation takes precedence to determine the values of the flow directions.
Water Virtual Flow - Seamless Provincial Data Set (WRIP, WFLOW): This data served to set the boundary extents for each watershed and was used as input into the DEM stream burning process and the correct flow directions for the Enhanced Flow Direction product. Each stream segment was coded with respect to which quaternary watershed they lie in. The time period includes the collection, creation, and updates made to this data set by CA's and other sources. Data collected from 01/01/1976 to 31/12/2008. The water virtual flow coverage is a line dataset that represents all of the creeks, streams, and rivers in Ontario captured at the regional scales of 1:10K for southern Ontario and 1:20K for central-northern Ontario. These lines are fully connected due to the virtual segments that run through lakes and double-lined rivers. These lines have the correct digitized direction which facilitates upstream and downstream tracing and analysis.
Canada Watershed Maps: Geogratis watersheds (federal) were used in northern Ontario where NRVIS data does not exist. These watersheds were seamed together with the NRVIS-based watersheds to complete the province. Data collected from active and discontinued hydrometric stations operated by Water Resources Branch. Data collected from 01/01/1972 to 01/01/2003. The Canada Watershed Maps depicts the primary, secondary, and tertiary drainage basins across Canada.