CHART SOUNDING MARKS

CHART SOUNDING MARKS Scattered over the water area of each navigational chart are many tiny figures, as in figure 9-7. Each figure represents the depth of water in that locality. Depths on charts are shown in feet, fathoms, or meters. A notation under the title of the chart provides the key to its depth; for example, “Sounding in feet at mean low water,” or “Sounding in fathoms at . . . .” Most charts also contain broken lines called fathom curves, marking the limits of areas of certain depths. A 10-fathom (60-foot) curve and a 15-fathom (90-foot) curve can be seen in figure 9-7. CHART ISSUE Charts used in the Navy may be prepared by the Defense Mapping Agency Hydrographic/ Topographic Center (DMAHTC), the National Ocean Service (NOS), the British Admiralty, or other hydrographic agencies. Whatever the source, all charts used by the Navy are issued by the Defence Mapping Agency (DMA). The Defense Mapping Agency (DMA) Catalog of Maps, Charts, and Related Products is a four-part catalog published by the Defense Mapping Agency Office of Distribution Services (DMAODS). It provides a comprehensive reference of all DMA maps, charts, and related products that are available for information. NOTICES TO MARINERS The chart and publication correction system is based on the periodical Notices to Mariners, published weekly by the DMAHTC to inform mariners of corrections to nautical charts and publications. This Figure 9-7.—Navigational chart showing depths and fathom curves. 9-6