Meteo-France has launched in 2002 a new weather radar programme with the main objective to improve the coverage of mainland France, especially for hydrological applications. This new programme includes 6 new radar sites, but also the replacement of 2 existing radars; besides, it will an opportunity to introduce in radar systems new technologies like dual polarization. This paper will focus on the approach that we have followed for the definition of new radar sites; the main steps are the analysis of the needs of hydrological and meteorological users, the use of numerical tools to identify possible radar sites and simulate the quality of the radar coverage from these sites. Finally, the technical and economic advantages and drawbacks of the different possible locations are compared as objectively as possible.