Flooding in Brazilian cities is seen as an environmental and social problem. This phenomenon is caused by soil sealing and mass urbanisation, which is happening in Brazil in a disorderly manner and without the necessary structural planning. The Preventive Civil Defence Plan has been used to define organisational measures for actions and responsibilities on the part of all stakeholders. Currently, the Geographic Information System is being used extensively to classify areas at risk of flooding. This study aims to calculate, using ArcGIS 10 software, the flood risk areas in the municipality of Tatui, weighted by the slope map and data on water accumulation during rainfall and urban zoning.