The Drift Thickness Map ( Maps- GeoServ ) shows the total thickness of Quaternary deposits covering bedrock. This map was produced by interpolating a continuous layer from control points derived from the Surficial Geology Map ( Maps - GeoServ ) and the Subsurface Database of the National Capital. The Surficial Geology Map provided control points where no data were available from the Subsurface Database. Areas mapped as bedrock outcrop on the Surficial Geology Map were assigned a drift thickness less than 2 m, as these areas may be covered by a thin layer of unconsolidated sediments. Areas that were mapped as Quaternary deposits were assigned a minimum thickness of 2 -3 m.

The Drift Thickness map indicates the average thickness based on inverse distance interpolation between control points; consequently, the reliability of the map depends on the distribution and proximity of control points to any interpolated thickness. The reliability of the map can be verified at any location by crosschecking with the Location of Control Points map. The stratigraphy and thickness at any location can be obtained by clicking on control point locations in the Subsurface Database