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Differences Between NM and LNM
While these two documents each contain important safety and general information for mariners and are each released weekly throughout the year, they are published by two different U.S. governmental agencies targeted at two different audiences. The Notice to Mariners (NM) is published by the National Geospatial-Intelligence Agency (NGA).  The Local Notice to Mariners (LNM) is published by each of the nine U.S. Coast Guard Districts.

Who reads each type of Notice to Mariners
The audience for the NM is the deep draft vessel plying U.S. waters or making a port call from overseas. The audience for the LNM is all vessels plying U.S. waters; that is, commercial and recreational, deep and shallow draft, vessels sailing offshore, in harbors, or along the Intracoastal Waterway.

Why is it Important to be Familiar with Both
The coastal waters of the U.S. are in a constant state of change. Channels are dredged and sometimes re-routed; new aids to navigation are established or deleted; new wrecks and obstructions are discovered; natural shoaling occurs in many areas; and new berthing facilities are built along the shoreline. In order for the mariner to transit safely, it is imperative that the mariner be familiar with all available information.

What´s the Source of their Information
Chart update information that is published in the LNM and NMs are derived from a variety of sources. Aid to navigation additions, deletions, and changes usually originate within the local Coast Guard District. Therefore, this information is typically transmitted internally between the Aids to Navigation unit and the LNM unit in a particular Coast Guard District. Since the Coast Guard maintains a network of stations throughout the country, chart update information may be reported directly to these units by a variety of local sources. For example, a Port Authority or a local boating group might bring a chart update item to the attention of the local Coast Guard. The Coast Guard LNM unit will then make a decision concerning whether a chart update should be published.

Over 95 percent of the chart update information that appears in NGA’s NM and the Canadian Notice to Mariners has already appeared in a Coast Guard LNM. Occasionally, a military unit will report a chart discrepancy directly to NGA and not to the USCG or NOAA. In this case, NOAA may first learn about the chart update by examining the NM. Likewise, it is only occasionally, that the Canadian Notice to Mariners contains unique chart update information that pertains to NOAA charts.

The majority of the chart update information that appears in the LNM and NMs first enter the charting pipeline through NOAA. The U.S. Army Corps of Engineers (USACE) is responsible for providing NOAA with survey information that pertains to federal channels and waterways. The Corps routinely conducts pre-dredge, condition, and post-dredge surveys in channel areas that serve as the main arteries for our nation’s ports. The latest information concerning depths in these federal channels is extremely important to deep draft vessels. This information is shown on NOAA charts through channel legends, tabulations, and by other means.

Over 25 Corps districts throughout the country provide NOAA with survey information concerning federal channels. NOAA cartographers analyze surveys and other information provided by the Corps to determine whether a chart update is required. In most cases, an update is required to notify mariners of the latest channel depths, channel re-configuration, or changes in adjacent depths. NOAA cartographers prepare these chart updates in an electronic form that is readily useable by the local Coast Guard unit responsible for publishing the LNM. NOAA cartographers also provide this information to NGA’s NM and the Canadian Coast Guard if applicable.

Other types of chart update information also enter the charting pipeline through NOAA. The USACE is responsible for issuing construction permits in coastal areas. NOAA receives these permits and monitors construction that ultimately may result in a change to the nautical chart. If the resulting construction is deemed "critical" to the chart, then this information will be provided to the LNM and NMs for inclusion. If the information is not critical, it will not be issued as a LNM or NM, but will appear on the next new edition of the chart. NOAA hydrographic field units and contractors conduct surveys in coastal areas throughout the country. If these field survey units find a critical chart discrepancy, they will report it directly to NOAA cartographers. This information will then be provided expeditiously to the appropriate LNM and NM publications for dissemination to the general public.

NOAA also receives chart update information directly from the recreational boating community. NOAA and the United States Power Squadrons (USPS) have had a partnership for over 40 years. The Cooperative Charting Program enables USPS members to report chart discrepancies by Internet throughout the country. NOAA conducts a similar program with the U.S. Coast Guard Auxiliary. If a chart discrepancy report is judged by NOAA cartographers to be "critical", it will be furnished for inclusion in LNM and NMs.

It should be noted that not all chart update information in NOAA’s possession is made available to the public immediately through the LNM and NMs. If new information is deemed "critical", it is always made available to the public through the LNM and NMs in an expeditious manner. However, if new information is not deemed "critical", it will appear only on the next new edition of the chart.
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