The underlying ground surface in urbanized areas is a key factor influencing the spatial structure of urban surface thermal field and the formation of the urban heat island. This presentation will demonstrate results from an investigation (that is partially supported by the Canadian Space Agency and also as collaboration with the EPiCC project) of the relationship between the spatial variation of the surface thermal field and the land surface characterization in two Canadian urbanized regions, the Greater Toronto Area and Ottawa-Gatineau. The relationships have been studied using comprehensive information derived from remote sensing (Landsat and Quickbird) and census data; these involved information layers include the surface temperature, land use, sub-pixel land cover density and population density. As background information, the near-surface air temperature records from weather stations in the two urban areas are also analyzed. Three aspects of the urban heat island thermal field are addressed, namely, (a) intra-city seasonal temperature variations, (b) the relationships among land use, urban land cover density, and population density and surface temperature and (c) the intensification of the urban heat island effect due to recent urban growth.