Research Paper 209, May 2007, vi, 69 pp. The Ontario government has recently taken a proactive approach to growth planning in the Toronto region, or Greater Golden Horseshoe (GGH). To carry out its policies, the Province needs reliable ways of measuring density and monitoring how it changes over time. This paper reviews the various definitions of density and discusses methodological and data problems associated with density measurements in the GGH. The authors examine existing density distributions in the GGH using 2001 census data, and analyze the densities of 10 sample census tracts. The authors note problems with using gross density for making comparisons between areas or time periods, and problems with using census data in density calculations. The authors recommend the delineation of small census tracts with permanent boundaries for the area of the GGH that is expected to build up during the next 20 to 30 years and the creation of a regional database on employment location, density, and output.