The science of the measurement and description and mapping of the surface waters of the earth with special reference to navigation WordNet 3.0 & Open English WordNet

Hydrography is the branch of applied sciences which deals with the measurement and description of the physical features of oceans, seas, coastal areas, lakes and rivers, as well as with the prediction of their change over time, for the primary purpose of safety of navigation and in support of all other marine activities, including economic development, security and defense, scientific research, and environmental protection. Wikipedia

The measurement of physical characteristics of waters and marginal land Wikipedia Disambiguation

Science which deals with the measurement and description of the physical features of the oceans, lakes, rivers, and their adjoining coastal areas, with particular reference to their control and utilization. OmegaWiki

The scientific measurement and description of the physical features and conditions of navigable waters and the shoreline. Wiktionary

Measurement and description of navigable waters. Wiktionary (translation)