This data set is a compilation of data acquired mostly by airborne surveys in Canada, gridded at 200 m and 1 km resolutions. The Geological Survey of Canada has flown or supervised more than 700 surveys since 1947, generally with a flight-line spacing of 800 m and an altitude of 305 m above the ground, though since 2000 the majority of surveys have been flown with a line spacing of 400 m or less. These aeromagnetic surveys have been leveled to each other to correct for arbitrary datums, slow variations of Earth's magnetic field over time, and differing survey specifications. The magnetic character of a rock depends on its ferromagnetic mineral composition, its concentration and its deformational and metamorphic history. Variations in the magnetic character of Earth's crust cause small magnetic anomalies in the earth's magnetic field. These magnetic anomalies can show geological trends and structural boundaries. The first vertical derivative of magnetic anomalies is calculated from the residual magnetic field and enhances the short wavelength component of the field. It is often used to trace contacts between magnetic domains. These data have also been published as two Geological Survey of Canada Open File maps: Magnetic Anomaly Map, Canada, (Open File 7799) and the First Vertical Derivative of the Magnetic Anomalies Map, Canada, (Open File 7878).