NOAA's New Nautical Chart Numbering System

Official US charts with chart numbers started with the founding of the US Coast Survey in 1807 that evolved through several forms into the modern NOAA. Historic charts can be tracked down at historicalcharts.noaa.gov.

The first Boston Harbor chart, for example, was called No. 337 in 1836. It was then replaced with No. 246 in early 1900s, and then in 1974 the system many of us grew up with was established. 

 

And then this chart was called 13270, a number that lasted until its final edition, when all paper charts were discontinued at the end of 2024.

That numbering system grouped charts using the first two digits as follows:

19xxx = Hawaii charts
18xxx = Pacific Coast and Salish Sea Charts 

17xxx  = SE Alaska

16xxx = Alaska 

14xxx = Great Lakes
13xxx = Atlantic, Long Island to Maine
12xxx = Atlantic, Cape Hatteras to N end of Long Island

11xxx = Gulf Coast and Atlantic up to Cape Hatteras 

To reminisce on this and learn all those chart numbers,  see  How to Get a Copy of a Discontinued NOAA Chart.

With the demise of the NOAA paper charts—which brought with it the end of all raster navigational charts (RNC)—the only official charts left were the electronic navigational charts (ENC). The "sunsetting" of the paper charts should not have been a surprise; it was announced in 2019 and they began the process almost immediately.

Many mariners first confronted ENC this year, but they are not at all new. They were defined by the IMO and IHO in 1990, approved for use in 2000, and they have been mandated to be used by all SOLAS vessels since 2018.

NOAA's first official ENC were published in 2003. The original NOAA ENC (now called legacy), some of which are still in use, especially on the West Coast, have wildly irregular shapes, and multiple scales (over 100!), that come about from the strict IHO rules on how they must match up and not overlap, yet stemming from existing paper chart data. Below is a sample from the Eastern Strait of Juan de Fuca.

Here we see legacy ENC along with the RNC (paper charts) they were based upon, plus the prominent lack of chart around Victoria BC, due to the IHO rule that no two nations can make an ENC of the same area. 

The shapes and scales of the legacy ENC are chaotic, but the file names (chart numbers) are in fact fairly systematic.

The chart number starts with the originator's country code (US) followed by the scale band of the chart, which is the compilation chart-scale range for legacy ENC, followed by the state abbreviation (USPS conventions), followed by two digits which is the chart ID, and that is followed by an "M."  No one seems to know why this is an M. We do know the full name according to IHO must be 8 characters, so they needed something. Some have suggested it means metric, but we do not need to be told that because all ENC, worldwide, must be metric, plus others have said there is no evidence this means metric.  The "no one," "some," and "others" refer to NOAA personnel, over the years.

So, for example, chart number US5WA16M means:

US    = United States made the chart

5       = scale band 5, which in legacy terms means 1:5,000 to 1:51,639

WA  = Washington state chart

16    = chart ID

M    = filler to make 8 characters

Note that ENC retain chart names (as opposed to chart numbers), similar to the paper chart names they were based upon. US5WA16M, for example, has the name "Approaches to Admiralty Inlet, Dungeness to Oak Bay."

Here are the scales in use

There is a detailed explanation of the rescheming program on line at Rescheming and Improving Electronic Navigational Charts.

The rescheming began slowly in late 2019, early 2020, which introduced a new numbering system, but it was not described on a NOAA website till mid 2024.  I have since discovered that it was indeed presented on an IHO website in 2017 and then updated at the IHO in 2020. 

The new chart numbering system was not noticed much because the rescheming was slow getting started, and we had most of the time just a few reschemed charts amid mostly legacy versions—as we have now in WA state.  But the rescheming is now nearly done elsewhere, and the new numbering has since been added to the latest rescheming overview. Recent rescheming progress has been very good.

There are still 8 characters to the name of every  ENC worldwide, and they still start with the national IHO Producers Code (US, CA, FR, GB...), followed by the scale band, but the meaning of the rest of the characters is new.

The regional code replaces the simple US state abbreviation, and the cell location within a matrix replaces the previous (chart number + M).  

In principle, and in some cases, this is a simple system. For example look at scale band 3 charts in Louisiana (LA).

The above are scale band 3 charts for LA with neighboring charts from TX, MS, AL, and FL.  Green ones are available now. Red ones are planned.

Many states, such as LA, have only one regional code, which is the state abbreviation + 1, LA1 in this case. So all charts in the state use regional code LA1. Other states like CA, WA, NY  have multiple regional codes, i.e., WA1, WA2, WA3, etc.

We see that the SW corner is cell location (A, A); they then increase to the north and east, ending when it reaches a neighboring regional code. 

It would be nice to stop at this point saying that is the new system, but that would leave out some details that might confuse us when encountered.

First, we note that for scale band 5, the regional code based on state ID can be replaced in the vicinity of some specific ports with its United Nations Location Code (UN/LOCODE). Also when multiple state codes are used, it is not always clear what the logic is for their specifications.  See for example, this plot of scale band 5 charts of NY.

These are scale band 5 for NY state, with some NJ, RI, and CT. The sizes are all the same, but the scales vary—in principle either 1:12,000 or 1: 22,000, but some of these have not been updated so they are still 1:10,000 and 1:20,000.

But looking at how they are named, we see the influence of the new rules.

NY has more than 1 region code, and on scale band 5 they use NY1, NY2, and NY9.  In California, scale band 5 uses CA1, CA2, CA3, and CA4, which appears to be latitude and scale band dependent. In NY, the codes seem to be longitude dependent, but not in sequence.

Also in NY we see the use of three UN/LOCODES: NYC (New York City), HEP (Hempstead), and PTJ (Port Jefferson). The location code abbreviations are likely understood by local mariners, but likely less so by visitors. Zoom in on the charts, and it should be clear what they refer to. 

Just about every city in the world has a UN code, which mariners might be familiar with on some level, because the ones that are ports are used in Type-A AIS voyage data for the reported destination. That AIS output is manually entered, and mariners can put what they want, but the intention is to use the UN codes, which is common. Looking at the practical side, however, many ships forget to change this once they leave a port. So often the destination broadcasted is actually where they just left from!

So the summary is, most ENC chart names still include the state, but it will be followed by a number whose whose meaning may not be obvious and may depend scale band.  

The exceptions are the scale band 5 charts that instead of the state regional codes, will (on just a few charts) use UN codes for what NOAA refers to as "Principal ports (based on cargo, fisheries, and tourism)."  NY uses three of these, one of which is certainly more "principle" than the other two. CA charts in production propose to use four of these: OAK (Oakland); NTD (Port Hueneme); LGB (Long Beach); and SAN (San Diego). One might not have guessed that Port Hueneme (why-NEE-mee) made the list, but we probably learn more about this port because of this.

The UN/LOCODES are also used in principle for scale band 6 ENC, but NOAA does not yet have any of these—and the couple we used to have are now discontinued.

The last point to address is the cell location ID at the end of the file name. It is based on a matrix, unique to the state and to the scale band, whose SW most cell is called AA.  In some cases, as above for LA scale band 3, the pattern is clear. In other chart regions it is not clear, and what we see in the SW corner is a matrix location that is not easy to decipher.

Below is a sample of where the DE and NJ charts meet.

The NJ charts look fine with AA in the SW corner, but the DE charts start with DE in the SW corner—which is just a coincidence that is trying to fool us! It has nothing to do with the state abbreviation. This is the D row of the E column, with the location of the non existent AE chart indicated here in red. This chart has not been created yet, but it might be once the legacy chart US5DE10M gets reschemed. 

And to see why this is AE instead of AA, we have to look to the NW. Delaware has charts running up the Delaware Bay, as shown below.

Again, the sequence of DE charts (blue) runs into a legacy chart (USDE13M) that has not been reschemed. Once that is done, we see where there might be a chart LA next to the existing LB, which would mark the A column that we can extend south to see the matrix location of a chart AA—if it were to exist. A key to understanding this cell location system is to realize that there does not have to be an actual chart for every location in the grid. Notice that FF is missing in the southern DE graphic.

So it seems that NOAA starts by defining an area that is going to be reschemed at, say, scale band 5. Then they lay a rectangular grid of scale band 5 charts over that area, which are labeled starting with AA at the SW corner. Then wherever they produce a chart within that grid, it gets the grid label for that specific location. In some cases the AA location will be a real chart, but in many others it will not.

Hopefully this helps understand the intended matrix system. 

So we have a new chart naming system that is better than the paper chart "eighteen-thousand means West Coast," and better than the legacy ENC system, which added a state designator, but the rest the name conveyed no information, and could be very misleading. 

In US5DE13M, shown above, for example, the same chart covers three different locations, separated by as much as 20 nmi, and adjacent legacy chart numbers had no relationship to each other. We knew that system had to go, and now it is nearly done. 

WA State Nautical Charts in Flux

All paper charts across the country were discontinued at the end of last year, leaving electronic navigational charts (ENC) as the only official charts. The shapes and scales of ENC, however, have been fairly chaotic for many years, but it has been planned to change this also for many years. The change is called "rescheming," which will standardize the scales and shapes of the charts, and eventually will also standardize the depth contours. 

At present (end of Oct, 2025) most charts have been reschemed, but only a few have been “metrified” — a NOAA term meaning the depth contours have been converted to a set of standard metric values.  All ENC have heights and depths in meters already, but the all important depth contours are so far only rarely converted. 

Here is a list of references on this process:

US Nautical Charting Plan

NOAA ENC Design Handbook

Rescheming and Improving Electronic Navigational Charts

Rescheming Status

Most of the US has already been reschemed and it is finally reaching into the Pacific NW.

Here is the present state of affairs for WA state charts.

This shows all charts in all scale bands. The scales vary from 1:10,000 to 1:180,000. They include mostly legacy ENC, meaning not reschemed, and a few scale band 4 reschemed charts.

Reschemed bands are defined by

This official NOAA table uses outdated terminology in that "Usage Band" should be called "Scale Band," and "Navigational Purpose" should be called "Usage Band."  Not the end of the world; but not at all useful—a chart name USWA430M means it it is a US chart of the state of WA with a scale band of 4, a number. Usage bands was a term describing paper charts, using the same words as used now, but completely different scale ranges.

WA charts are all less than 49º Lat so new ones will all be made square with regard to distance, ie a scale 4 chart will be 0.3 x 60 = 18 nmi tall and 18 nmi wide, but it will still appear as a rectangle on a mercator chart, with the width to height ratio being the cosine of the latitude. At 47º, for example, width to height on a mercator will be cos(47º) = 0.68.

Here we can see how the legacy scales are being changed from a range of values to just 2 specific values for each band... which seems good progress, but it was not long after making that decision that NOAA decided to change these values to match the proposed new S-101 scales, which are now the new NOAA standard. 

This has meant that most of the earlier reschemed charts at 1:20,ooo and 1:10,000 (Scale Band 5) have to be redone to be 1:22,000 and 1:12,000. That is a transition now in process. The same is true for  Scale Band 4 (1:40,000 and 1:80,000 ) now getting changed to 1:90,000 and 1:45,000. This will not affect the WA charts, because that decision was made before they got to the WA charts in the first place.

The legacy column is a range of scales, but the reschemed options are just two.
See also note in above image above about Scale Bands.

Looking more closely at WA state charts by Scale Band at present:

These are Scale Band 5, which are all legacy except for along the Columbia River, which is covered by a series of 1:12,000 reschemed charts.

We have no Scale Band 6 (Berthing) charts in this region.

We have these three Legacy Scale Band 3 charts

And as of a couple months ago we now have several new Scale Band 4 charts at 1:45,000.

The four irregular shaped charts above (NW most) are the remaining legacy Band 4 we have.

_______________

Now we can get to the punch line: what will this look like sometime next year? Here is that plan for this area...

There are two chart sizes, the larger ones are 1:90,000 along the coast and west of Port Angeles, and 1:45,000 inside of PA. The smaller charts are all 1:12,000.

We see here obvious progress in chart organization, but with a potentially serious step backwards with regard to charting along the coast of Canada—implied by the gap below Vancouver Island. At present we have that coast all covered with ENC (see above) except for the area around Victoria, for which we need just one Canadian chart, CA470075. 

We are up against an IHO rule that a region of adjacent national waters can only be created by one nation, which is what left that gap in our ENC for Victoria, BC.  But US-Canadian hydrographic relations have been in question since 2020, when hydrographic data stopped being shared. So we do not know what is going to take place along that border in the future. At present, no one at NOAA answers emails presumably related to the government shut down. If we learn anything about this, we will post a note.

In the meantime, it seems valuable to download the existing ENC for all of the Strait of Juan de Fuca and San Juans that border on Canada so you have charts. Using qtVlm this is an easy task, just draw a box around the southern half of Vancouver Island and open the NOAA catalog to see what is there and to download the charts.

The charts we want to preserve for back up are: US4WA 30M, 31M, 34M (80k), and 36M (100k) plus US5WA 43M, 44M, 41M (25k)

qtVlm Training Mode — Available to all Schools

We designed the Training Mode supplement to qtVlm to be available to all schools that teach marine navigation or weather. The getting_started link explains how to install it for Mac, PC, or mobile devices — with the note that qtVlm is free for Mac or PC computers, but to run Training Mode on a mobile device requires the paid version of qtVlm mobile (iOS or Android), which as of Oct, 2025 is $49.

We recommend getting started with qtVlm on a computer, then when ready to use it underway you can wirelessly transfer all the set up information to a mobile device with its new Data Exchanger function.

In this note we will go over what is included in the Training Mode and explain how to get started using its contents. The Training Mode install does two things to your installed copy of qtVlm:

(1) Assigns several optional settings

(2) Installs several data sets for navigation and weather work

 

Assigned Optional Settings Examples

Any of which can be undone to meet user's preference.

• Changed the water color from dark blue to white. This makes a few of the weather data overlays or image overlays easier to view. 

• Minimized the toolbar icons to ones we need at first, knowing we will want to add others back later in the training.

• Choices have been assigned to dozens of other optional settings, such as extent of the COG predictor, set to start at 6 min; length of the heading line, set to start at half a mile (926m), colors and thicknesses of these two lines, depth contours that control alarms and water colors, instrument display options (size and location of selected meters, etc), and so on.  All easy to change as desired. 

Here is an example, showing optional instrument displays (qtVlm has many options for meters, dials, graphs, etc), but we start very simple for basic speed and course meters:

To see details: click it, open image in new tab, and zoom.

Install Environmental Data and Data Links

• qtVlm is an international product, so it does not come with US tidal harmonics installed. We have videos on how to do that, but we do this in advance for the  Training Mode.

• State of the art tides and currents, however, are not the NOAA harmonic values at a few selected locations, but rather the Operational Forecast System (OFS) that provides high res digital forecasts across the chart. We included two links to this live data, one for San Francisco Bay and one for Chesapeake Bay. These files provided by qtVlm also offer unique data on actual water depth at each location on the chart, which can be used for very realistic navigation simulation, plus the OFS forecasts are a way to demonstrate the limits of the harmonic predictions.

• We also include custom link to NCOM currents, which are typically better than the ubiquitous RTOFS global values for waters adjacent to the US.

• To get a quick start on weather work, we include three preloaded GRIB files: HRRR and GFS model wind and pressure data, plus the Salish Sea OFS tide and current data for the same region, so routing and simulations can be practiced.  Later users can, of course, display GRIB files from external sources or use their direct connections to XyGrib and to Saildocs from within qtVlm.

Pre Installed Charts

• qtVlm focuses on official electronic navigational charts (ENC). It has one of the best presentations of these charts of all navigation software, including the very expensive ECDIS units used on large commercial and governmental vessels. As it turns out,  qtVlm also has a state of the art built in system for selecting and downloading US charts, but to save some time several have been loaded.

• Several scales of charts in the Pacific NW are included, as well as several samples in other parts of the country to seed the NOAA catalog function for further download — of charts from your local waters, for example.

• Also included are two raster navigational charts (RNC) as samples, one for 18456TR that we use in the Starpath Inland and Coastal Nav Course and also 1210TR which is used in many of the ASA navigation courses.  The US no longer produces RNC, but other nations do, so it remains of interest to have a look at these, plus piloting exercises from nav courses can be solved with them.

• qtVlm lets users store 4 screen/chart layouts (F9, F10, F11, and F12). We have preset F9 = start up view and F10, which are sample NOAA charts on the East Coast.

Special IHO Resources Included

• The International Hydrographic Organization (IHO) creates several custom products that are useful for learning ENC. One is called ECDIS Chart No. 1. This is a set of ENC showing all ENC symbols. It is a good place to review and compare symbols. Just like paper chart symbols, some that are very similar have notably different meanings. The dozen or so ENC for this presentation is hidden in the desert near Timbuktu, Mali!  There is a mark assigned to the location so we can get there quickly from any place in the program.

Note: there are no marks in the Marks Management list in the initial Training Mode, but they are in the Archives. So open Archives and choose load into qtVlm.

• More interesting still, is the IHO has created a make-believe island group off the coast of Madagascar. The multiple ENC for this region, called Micklefirth, includes all the possible official ENC symbols, including, areas, lines, and point objects presented in a realistic setting. It is a great way to study the intended uses of the symbols. The IHO made these ENC as a way for navigation apps to check that they are presenting the symbols properly, but we can use it for whatever we like.

Owlswick Harbor in Micklefirth.

So that is most of what is included in the Training Mode. Schools can use these resources as they see best. Advanced instructors can also create their own Training Mode if they need something different.  

On the other hand, once the program is learned, which does not take long with instruction and the support resources available (Manual, Cheat Sheet, PlayList, English FaceBook), it is easy to change all the configurations, and to load all resources from built-in or primary sources.  The Training Mode is just intended to make the initial introduction a little bit easier.

Note that once the Training Mode has been loaded, the menu item shows these options:

Download and activate will take you back to the initial configuration of the Training Mode.

Deactivate closes the Training Mode but saves all the changes you have made.  You will then have the option to Reactivate Training Mode bringing back the configuration you you had, or you can then also choose to Uninstall Training Mode, which takes you back to the base configuration you had before installing the Training Mode.

Uninstall Training Mode does just that. All trainings settings will be lost and only option is to start over from scratch with a new Training Mode install from the getting_started page.

Later we will add sample videos on how we use these tools in our courses.

Here is a video illustration of the topics listed above:

qtVlm Training Mode: Overview and Content (22:10)

Shared Remote Simulation with qtVlm

A unique feature of qtVlm that is a powerful training tool is its ability to share AIS positions amongst simultaneous users. We can have, for example, three users in different parts of the world agree on a time and place to meet up for a practice sail. To do this we need to have the three (or ten!) users set up the program in the same way. Each will then drive their own boat, but see on the screen the other boats taking part.  We will turn on collision avoidance setting in AIS to see how that works as well.

We can do this with a canned environment by forcing a fixed wind and fixed current, or we can share the same model forecasts for wind and current. The Training Mode includes wind and current for a section of the Eastern Strait of Juan de Fuca, between WA state and Canada, so we will use those for the example.

These are text notes for the process, followed by a video demo of the operation. Here are the settings that need to be the same for all participants:

1) Same polar loaded. We can use the default classic 40 version.  These could be different but if we want to race it would be more interesting if all the same.

2) Same GRIBS loaded. In the Training Mode, you can load the HRRR wind in Slot 1 and the OFS current forecasts in Slot 2.

3) These environmental data overlap starting at 4/11/2025 at 15:00:00 UTC. So after loading the GRIBS, use the clock icon to set the Grib time to that value. (If needed, go to Config/General/Units, and choose UTC.) 

4) Since we are not using live data, we also need to tell qtVlm when we want to start the simulation. This is done under menu Boat/Boat Settings/Navigation Simulation Mode. Force the starting time to 4/11/2025 15:00:00 UTC.

5) It might be helpful, but not crucial, to display the Grib time slider in the Grib Config window. If it does not look like this, then something is wrong. Do cmd+I or ctrl+I to see what is loaded. 

Check in the Grib config/Corrections window to be sure you have no forced wind or current. That will override the Grib data.

6) For simulation and real sailing it is valuable to turn on the Microboard (this is not on in the initial Training Mode configuration). Menu/Config/Boat/Show microboard.

7) We might also share 3 marks to show where we should start our boats. If we are not mindful of this, we could run into each other quickly, which ends the simulation. Here is a sample. None of this has to be precise.

8) When you start the simulator, the boat will start head to wind, so it will not be moving. If you are moving, then the engine is on. Check Boat/Boat Settings/Engine and Tacks/Gybes.  Be sure both are set to 0.0.

9) We also need to set up the AIS configuration to make this work. Menu/qtVlm Config/AIS to see this:

And we need to turn on the AIS from the tool bar:

AIS icon must be green.

Then we should be ready to go, and each participant can start the simulation and it should look something like this, keeping in mind that it takes a minute or two for the actual AIS vessel name to show up.

Note in the Seattle screen above, he has a COG predictor cone turned on and we are sitting head to wind in a current, so he is drifting backwards.  All the boats are doing this, but only this one has that turned on.

In principle we could agree to a boat set up and a chart, etc. But once this is running there is much to learn and practice with.

Here is a look at the three computers running the simulation. 

Later we will discuss the various program controls we can use to optimize sailing routes.