In hydraulic modelling of floods, one of the most fundamental input data is the geometric description of the floodplains and river channels often provided in the form of digital elevation models (DEM). During the past decades, there has been a significant change in data collection for topographic mapping technique, from conventional ground survey to remote sensing techniques. This chapter continues the presented line of research and deals with the assessment of the effect of using different DEM data source and resolution in a 1-D hydraulic modelling of floods. In hydraulic modelling, multiple sources of uncertainty can emerge from several factors, such as model structure, topography, and friction coefficients. Different models were built by using them as geometric input data. The chapter also showed that, to support flood inundation models, the quality and accuracy of the DEM is more relevant than the resolution and precision of the DEM.