Atmospheric corrosivity maps are essential tools for users or designers since they can provide thickness loss data and corrosivity levels in different regions. In order to understand the corrosive behavior of bare and hot-dip galvanized steel, atmospheric and environmental primary data were collected throughout a 1-year exposure test period at 11 locations across Thailand with additional secondary data from 44 locations from the Thai Meteorological website. Since the thickness loss of the steel correlates with the atmospheric parameters and environmental pollutants, two dose–response functions were established for the central region and for the northern and northeastern regions of Thailand. The dose–response function is able to establish the thickness loss of steel at the 44 locations that have atmospheric and environmental data. Finally, the inverse distance weight method was conducted in order to create the corrosivity map. The results indicate that the thickness losses predicted from the dose–response function are not far different from the atmospheric exposure test results. The atmospheric corrosivity map can effectively provide the thickness loss information for each type of steel throughout the map.