The Centre for Topographic Information (CTI) jointly produces the CDED with federal, provincial and territorial government agencies as well as the private sector.
A CDED consists of an ordered array of ground or reflective surface elevations, recorded in metres, at regularly spaced intervals. The source digital data for CDED is extracted from the hypsographic and hydrographic elements of the National Topographic Data Base (NTDB) at scales of 1:50 000 and 1:250 000, or the Geospatial Data Base (GDB), or various scaled positional data acquired by the provinces and territories, or remotely sensed imagery.
Purpose:
CDED plays the same role as contours and relief shading on conventional paper maps. CDED serves as a key primary data in a range of applications critical to achieving sustainable development.
These applications include environmental and ecological impact assessments, water flow and water quality analysis, climate change studies, forest regeneration planning and wildlife habitats.
In addition, CDED can be used in the generation of three-dimensional graphics displaying terrain slope, profiles and line of sight. Non-graphic applications include geoid calculations, terrain modelling, flood simulations and telecommunication studies.
Canada's coastline, oceans and estuaries at mean sea level, are assigned an elevation value of zero metres. However, the Nova Scotia coastline, oceans, and estuaries are depicted at the mean high water level (MHWL), which has varying elevations across the province. All MHWL elevation values are with reference to the Canadian Vertical Geodetic Datum 1928 (CVGD28).
For CDED produced using ground elevations, water bodies are naturally occurring areas of constant elevation (lakes) or having a small slope (rivers). Water bodies are assigned their known elevations or estimated values. Lakes are represented flatter and lower than the surrounding terrain (one elevation per lake) and the shore must be clearly discernible. A water body of unknown elevation is assigned an interpolated elevation that is at least one metre lower than the contour elevation surrounding its shores. Drainage (rivers and streams) must be continuous (no gaps), have constant water flow and a descending order of z-values.
For CDED produced using reflective surface elevations, water bodies (lakes) may not have a constant elevation. They may have a small slope to indicate the direction of the water flow.
Quality control must assure that the CDED is smooth within the grid and continuous from node to node, except at natural break points such as streams, cliffs, and craters.
Completeness Report:
The content of the CDED1 data sets is constant since the number of elevation points per profile and the number of profiles per cell are constant for all CDED1 files (1201 x 1201).
Positional Accuracy:
Horizontal Positional Accuracy:
Horizontal Positional Accuracy Report:
Accuracy evaluation is related to the data source(s) used to generate the CDED.
National Topographic Data Base Data Source: Planimetric data accuracy is expressed as the circular map accuracy standard (CMAS) of topographic feature derived from the equation below: Standard circular error: σc = 0.7071 √(σx² + σy²) σx = standard deviation in the X-axis σy = standard deviation in the Y-axis Circular map accuracy standard: CMAS = 2.1460 σc.
Circular Map Accuracy Standards (CMAS) for NTDB sources from Centre for Topographic Information (in metres).
Vertical Positional Accuracy:
Vertical Positional Accuracy Report:
Accuracy evaluation is related to the data source(s) used to generate the CDED
National Topographic Data Base Data Source: Altimetric accuracy of source material is expressed as the Linear Map Accuracy Standard (LMAS) in the same measuring unit method of NTDB data, obtained according to the equation below: Linear map accuracy standard: LMAS = 1.6449 σz σz = standard deviation of the elevation.
Linear Map Accuracy Standards (LMAS) for NTDB sources from Centre for Topographic Information (in metres).
Lineage:
Source Information:
Source Citation:
Citation Information:
Originator:
Government of Canada, Natural Resources Canada, Center for Topographic Information
Publication Date:
1999-01-18
Title:
National Topographic Data Base - 072O15-3.0
Source Scale Denominator:
50000
Type of Source Media:
Digital
Source Time Period of Content:
Time Period Information:
Range of Dates/Times:
Beginning Date:
1988-01-01
Ending Date:
1988-01-01
Source Currentness Reference:
publication date
Source Citation Abbreviation:
NTDB - 072O15
Source Contribution:
The hypsographic and hydrographic elements of the source NDTB were used to produce the CDED. Special care was taken with regard to watercourse direction of flow and the flatness of the water surface.
Process Step:
Process Description:
The following steps were undertaken to generate CDED derived from 1:50 000 NTDB source data:1) Flow directionality is applied to the stream coverage using the lake and contour data (arcs pointing downstream), maintaining a connected hydrographic network.2) Incongruities in the NTDB hydrography and hypsography including the problems in the edgematching with the 9 surrounding tiles are identified and corrected.3) Elevations on lake polygons corresponding to the lake elevations recorded on the paper map are tagged.4) A DEM using ANUDEM version 5 with hydrographic network, contours, and elevation points as input data, are produced.5) Quality Control on the DEM is conducted.6) The DEM is converted to CDED format. For the final CDED, an automatic inspection is conducted by the Centre for Topographic Information Sherbrooke prior to archiving.
FGDC Content Standard for Digital Geospatial Metadata
Metadata Standard Version:
FGDC-STD-001-1998
Metadata Use Constraints:
Only the English XML metadata file is valid according to the XML (W3C) schema as defined by the Federal Geographic Data Committee (FGDC) (http://www.fgdc.gov). The French version of the XML metadata file does not respect the domain of values, which is only available in English in certain fields, and exists solely for the presentation of information.
Users must ensure that they use the FGDC XML schema with the English version of the XML metadata to validate the metadata.