水文地理学是研究水的性质、分布、循环、运动变化规律及其与地理环境、人类社会之间相互关系的科学。地球表层的水，经过约35亿年的积聚和演变，逐渐形成了今天的水圈。水圈中的水广泛渗透于地球表面的岩石圈和大气圈，积极参与地表的各种物理、化学过程，不仅改变了岩石圈的面貌，也使大气圈的大气现象变得复杂多样，而且导致生物圈的出现，从而水又积极参与地表的生物过程。水对地理环境和生态系统的形成与演化具有重大的影响。

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 defence, scientific research, and environmental protection.