Name the largest urban centre for each river basin it is classified as being in. Urban centres are defined by the European Commission at the link below. Occasionally an urban centre name isn’t a city name, but rather a country/district/area. River basin and population shown. FYI – river basins are often very large areas around a river, and the city may be a good distance away from the actual river.

https://ghsl.jrc.ec.europa.eu/ghs_stat_ucdb2015mt_r2019a.php