Over the past 80 years, the Rhine-Meuse delta has been mapped extensively by drilling boreholes. These maps are compared with a new detailed digital elevation map of the Netherlands (AHN) that became available in 2004 and is based on very accurate, (sub-decimeter) laser-altimetry data. Examples show, that existing maps can be significantly improved. However, field checks remain a necessity. Therefore, the AHN-data need to be confronted with existing borehole descriptions using a GIS. Geomorphological analysis and geological interpretation of surface elevation patterns now enable us to map larger areas, in greater detail, with greater accuracy, and much faster. It is argued that detailed (≥1 : 50,000) geological mapping of the Netherlands should be resumed, combining the databases of Utrecht University, the National Geological Survey and Alterra.