The problem considered in this article refers to such representation of data from an electronic navigational chart that fast and effective identification of areas meeting certain criteria, e.g. depths, will be possible. This is of importance in such processes as situation analysis and assessment or the determination of a safe trajectory of ship movement. The recurrent algorithm for area discretization herein presented makes use of the trapezoid mesh. Its properties and requirements, as well as the methodology of area discretization are presented. The results of an experiment based on that algorithm are describe