Abstract. Assessments of natural gamma radiation were done for urban sites in the city of Ribeirão Preto -SP -Brazil, allowing to infer the average annual effective dose value for the population in these areas. The measurements were done using a vehicle with a mobile radioactivity measurement system, Eberline, with a plastic scintillation detector and a Global Position System (GPS), to collect measurements of gamma dose rate and its spatial distribution. Using the national census information, the stored data allowed mapping the radiometric measurements through the ArcGIS software, correlating the geographical coordinates with their respective dose rates. These maps illustrate how effective dose values are distributed within the selected areas and also correlate the collective dose values for these populations. Around 45,000 georeferenced effective dose values, ranging from 12.2 up to 59.8 nSv/h raised an average value of 0.034 ± 0.004 mSv/year, which is less than the worldwide average effective dose value of 0.07 mSv/year [12] (for outdoor exposures from terrestrial radiation sources) and less than the previous average values found in Brazil for the regions of Poços de Caldas, Guarapari, Andradas, Caldas and Meaípe [2,10].