The Subsurface Database ( Maps - GeoServ ) of the National Capital Area contains information on the nature and thickness of unconsolidated sediments overlying the bedrock. The information was compiled from engineering borehole logs, water well records and shallow seismic surveys. Since the information is coming from various sources and originally collected for different purposes, the terminology used to describe the geological units and the amount of information varies greatly from one source to the other. Consequently, it was essential to standardize the terminology and parameters in order to obtain a more homogeneous database that could be used not only for site-specific information, but also to generate maps and graphics at a regional scale. Even though the database was verified extensively, it must be expected that it contains some compilation or interpretation errors, such as wrong locations or incorrect stratigraphy. The database contains only boreholes that reached bedrock, and the last update was done in 1994.