In 2019 NOAA announced plans to end all production of Raster charts, both paper and digitized copies by January 2025. NOAA is ending support for Raster charts to focus their efforts on support and enhancement of their Electronic Navigation Charts or ENCs.
In the Beginning
NOAA started producing electronic charts in the 1990’s as tracings of paper charts. These early ENCs, also known as Vector Charts, were designed for use on first generation chartplotters with limited memory and processing capability. To keep the size and complexity of these ENCs manageable, not all of the information on the paper chart was entered into the ENCs. Early adopters and users of these ENCs were large commercial ships that could afford the expensive electronic equipment to display and use the ENCs. Early electronic charts catered to ocean-going vessels transiting commercial shipping routes. Over time, chartplotters became more capable and more affordable for recreational boaters. Today, most recreational boaters rely on chartplotters and their ENCs.
Since ENCs started as traced images of paper raster charts of various sizes and scales, the resulting ENCs were and are a collection of various sizes and scales. Today there are over 1600 irregularly shaped ENCs in over 100 scales. Most of the ENCs lack detail of the upland areas that can be found on the corresponding raster charts.
Enhancing Legacy ENCs
NOAA continues to enhance existing Legacy ENCs by adding elements that were originally omitted to keep the charts’ file size manageable. NOAA plans to update and enhance Legacy ENCs until new next generation Reschemed ENC charts are available for that area. In areas where Legacy ENCs are not available or do not adequately provide chart information, existing digitized raster charts are being updated with safety related changes.
As new reschemed ENCs are available, NOAA will issue six-months advance notice of raster charts that are due to be canceled and no longer supported.
Reschemed ENCs – Standardized Scales
Reschemed ENCs are the new electronic charts replacing Legacy ENCs and raster charts. These charts are created at various scales for different navigational purposes. The smallest scale (least detailed) “Overview” charts are used for basic voyage planning. The largest scale (most detailed) “Harbor” and “Berthing” charts are used for navigating into harbor and maneuvering to a pier or wharf. Reschemed ENCs are categorized into six usage bands, or Scale Bands.
The new ENC scheme uses 11 scales, two each for Scale Bands 1 through 5 and one for Band 6. The table below compares the scale ranges of the old ENC scheme to the new standard scales for reschemed ENCs.
Standard ENC cell shape and size
The new ENC layout consists of nested cells with boundaries that follow lines of longitude and latitude. Sixteen larger scale ENC cells fit inside one cell of the next smaller scale band. The figure below shows how sixteen (16) Band-3 cells (green squares) fit inside one Band-2 cell (brown) and the relative sizes of the other Bands.
Reschemed ENCs will bring more consistent scales; and in cases, may bring larger scale coverage. When the scale for coverage in the original legacy charts is not consistent with one of the reschemed standard scales, the scale for the newly created ENC will be at the next larger scale. Standardized scales for newly created reschemed ENCs also facilitates resolving discontinuities and “edge-matching” inconsistencies with adjacent ENC cells.
International standards call for depths in ENCs to be expressed in meters, not feet or fathoms. When the Legacy ENCs were created, paper chart depth contours measured in fathoms and feet were left in place and converted to meters; often in fractional meters. With the reschemed ENCs, all depth contours will be compiled in whole metric units. However, some newly reschemed ENC cells will not be recompiled in their first edition release. Soundings less than 30 meters are stored and displayed as meters with subscripts in tenths of meters.
Below is a table, Scale Band, with the standardized depth contour intervals that will be used in reschemed ENCs.
Rescheming Progress and Status
NOAA’s original timeline included a completion date of January 2025. Below is a map showing the original timeline for completing reschemed ENC charts for different geographic areas. At this time NOAA has made good progress but are lagging behind their original schedule. NOAA has not yet revised their schedule; all indications suggest that the process is one to two years behind the original schedule.
Image Credits: NOAA