The horizontal gradient of gravity anomalies map of Canada shows variations in the gravity field caused by lateral variations in the density of Earth's crust and upper mantle that reflect differences in composition and thickness. Systematic gravity mapping began in Canada in 1944 and is ongoing. All Canadian gravity data are tied to the International Gravity Standardization Network 1971 (IGSN71) to create a coherent dataset at the global scale. Local gravity anomalies result from the juxtaposition of relatively high- and low-density rock types. The horizontal gradient achieves local maxima over or near contacts between rock units with different density.