Due to its concave topography, the climate in the Rouen region is affected by the impact of urbanization. The urbanized area occupies the bottom of the Seine Valley and extends onto slopes and plateaus. These topographic conditions contribute to the formation of well-differentiated local climates. To better understand the urban heat island, an expeditionary measurement campaign was carried out from 25 June to 11 August 2020. This campaign is based on the knowledge of the spatial distribution of temperatures in the city. These measurements were carried out according to different profiles and a specific programme. During this period, the region was affected by three heatwaves.. In this study, we present the results regarding the air temperatures obtained on 25 June 2020. The study also relies on the analysis of “Landsat 8” channel 11 satellite images, with a spatial resolution of 30 m to define surface temperatures. The results obtained during the measurement campaign show the importance of the differences between vegetated and built spaces. They also highlight hotspots (at traffic intersections and on main transport corridors – boulevards). The results obtained from the processing of satellite images show significant temperature differences between the industrial area and the rest of the city. There is an important thermal contrast between green spaces and asphalt squares in the city centre. There is a thermal lag between the “west” plateau, Cailly Valley, and the rest of the city.