Bathymetry Line

Data Format(s): Bathymetry Line

Coordinate system: Grid CS = Universal Transverse Mercator; Map Proj = Transverse Mercator; Horiz. Datum = NAD83; Vert. Datum = CGD28 - CDN

Over the course of 50 years the Ontario Ministry of Natural Resources and Forestry (OMNRF) has captured bathymetry data for over 10,000 lakes across Ontario. In 1968 the Department of Lands and Forests initiated the Aquatic Habitat Inventory Program to collect information for Ontario’s inland water data. One product was a series of contour maps showing lake depth. In many cases, these maps still represent the only authoritative source of bathymetry data for lakes in Ontario. These maps have been converted to digital GIS data which has resulted in the vast majority of the current data in the Bathymetry Line data class. More recent bathymetric data has been collected using sonar and GPS technology. This modern technique creates lake depth points (spot depths) rather than contours. This point data is stored in the Bathymetry Point data class. Bathymetry Line contains lines of constant depth called depth contours or isobars. Depth contours are used to describe the terrain relief below the surface of the water. The data used to derive the depth contours are always spot depths but the density and positional accuracy of these spot depths vary depending on the survey style and parameters. Before GPS data was available, spot depth locations were derived by straight line transects across a water body which were then plotted on a map. The time consuming nature of this method limited the number of transects collected. Now GPS data collection is not limited to transects and therefore spot depth collections tend to be far denser with greater horizontal accuracy. Depth contours have been derived in one of two ways: 1. Visually interpreted and drawn by hand based on transects of the water body 2. Interpolated using GIS processes such as Kriging or Natural Neighbours Vertical accuracy of the data varies greatly depending on the density of spot depth collected for each lake. Horizontal accuracy will also vary greatly on older transect based collections but will be within 5m for GPS based collections. Bathymetry point and line data should not be used for navigational purposes. For more information visit