Getting a handle on the various kinds of nautical charts is one of the most practical steps you can take before heading out on the water. Modern marine cartography has come a long way, giving us specialized tools tailored specifically to the unique demands of marine navigation. Whether you are prepping for a quick afternoon sail or a multi-week ocean crossing, knowing your tools keeps everyone safe.
Nautical chart types:
● Navigable charts: The complete source of information on the oceans and waterways of the world, highlighting water depths and shorelines. If you want to dig deeper, our guide on Understanding the New MOHRE Law in the UAE (2025) covers this well.
● A pilot chart: Your main reference for historical weather trends, wind patterns, and ocean currents.
● A scaled-down chart: Also known as a planning chart, perfect for mapping out big-picture ocean voyages.
● A large scale chart: Built specifically for coastal cruising and general approaches where hazards are closer.
● The harbor chart: A comprehensive document providing micro-level details for docking and tight spaces.
Between these various chart types, there are distinct differences in scale and purpose. Throughout this guide, you will learn about all types of nautical charts available today, including both paper and electronic formats.
Which Type of Chart Is Right for You?
Most of the time, sailors refer to navigation charts simply when they speak of charts. These specialized maps convey detailed information about water depths, bottom features, and dangerous shoals that are vital to safe harbor navigation. They function much like standard road maps do for drivers, but with a heavy emphasis on what lies hidden beneath the surface.
There are several other types of charts that can help sailors plan their routes and passages besides standard navigational charts. Choosing the right one depends entirely on how far offshore you plan to travel and what kind of vessel you are running.
Navigational charts
Navigation charts are most commonly referred to as nautical charts by professional mariners and recreational boaters alike. These serve as your primary blueprint for exploring unfamiliar ocean maps and complex waterway systems.
Because boats do not travel on paved roads, comparing a highway atlas with a marine chart is never a valid comparison. You can investigate highway routes and street names on land maps, but you cannot navigate off-road using them. A standard land map might completely ignore underwater hazards or depth contours because its focus is purely terrestrial.
Unlike a topographic land map, the terrain contours and geographical features such as underwater ridges, valleys, and shallows are clearly shown on a marine chart. The Navy and commercial fleets use nautical charts to identify safe deep waters and hidden underwater obstacles. It will be helpful to sailors who always sail outside of the beaten path and need to know how the water flows beneath the keel.
Understanding how to read and access accurate navigation charts is just as important as knowing what they show. Whether you are planning a voyage or updating your onboard resources, having the right legal and technical tools is essential for compliance when choosing local marine experts or navigating complex maritime regulations. For mariners looking to access official navigation resources, official hydrographic agencies provide a wide range of paper and electronic options that meet international safety standards.
In contrast to simple road maps, marine charts contain extensive data on navigational aids such as buoys, daylight markers, lighthouses, and daybeacons. These permanent features help you fix your exact geographic location when electronic systems fail.
We will examine more fully the distinct options available for paper and electronic navigation charts.
The Pilot Chart
Pilot charts are useful for sailors planning long voyages across vast stretches of open ocean to pick the most appropriate weather route and departure time. Rather than showing water depths, these sheets focus heavily on atmospheric pressure, wave heights, and prevailing gale frequencies.
By compiling rough predictions of historical weather conditions gathered over hundreds of years, pilot charts offer a statistical outlook rather than a daily forecast. In addition to providing planners with wind and current data, meteorologists use these historical probabilities to help transoceanic skippers avoid dangerous seasonal storms.
The scale of the chart
You can interpret a chart contents properly only by looking at its baseline scale information. A chart most important characteristic is its scale, which dictates how much physical territory is represented on the page alongside descriptions of depth in feet, meters, or fathoms.
Scales on all nautical charts are expressed as mathematical ratios. Some are 1:2,500 for tight harbors, while others are 1:1,000,000 for open ocean passages. Specifically, this is the ratio between the distances shown on the chart and the actual distances in real life. The size of an inch on a chart with a scale of 1:25,000 is the equivalent of 25,000 inches in real life, regardless of how you measure it.
Charts with small scales
These charts are often referred to as sailing charts, general charts, or planning charts, and they offer the smallest amount of detail while covering massive geographic areas. For general charts, the scale can be around 1:500,000, while sailing charts usually range between 1:100,000 and 1:500,000. A small scale chart typically features the following traits:
● A greater scale error and a reduced level of fine detail for local hazards.
● Designed specifically to plan long-distance ocean trips and offshore passages.
● It contains major government markings or offshore hazards, but leaves out minor local markers.
● Larger scale harbor insets may be blanked out or referenced separately.
● They are completely unsuitable for approaching unfamiliar harbors or navigating close to rocky shorelines.
● Since broad hydrographic surveys cover such massive areas, they are not updated as frequently as coastal maps.
● There is a range of positional errors for objects, running from 450 feet up to almost one mile on the smallest scale maps.
The Large Scale Chart
A coastal sailor is most likely to be interested in coastal and approach charts due to their high level of localized detail. These high-resolution maps provide a much better view of hidden rocks, shallow bars, and local navigational hazards with scales chosen between 1:25,000 and 1:100,000.
Most weekend trips that do not take you too far from home port will be mapped out using these specific coastal charts. They strike a balance between broad overview and actionable local intelligence.
● Unlike small-scale charts, these provide high detail while still omitting minor clutter to preserve visual readability.
● Ideal to plan trips along rugged coastlines or to successfully finish a long offshore journey.
● Bound collections known as chart kits commonly bundle these coastal maps together for regional cruising.
● Notices to Mariners should be applied frequently to keep these active navigation aids up to date.
● On 1:100,000 scale charts, positional scale errors are typically much smaller, ranging between 25 feet and 100 feet.
A harbor chart
In large-scale harbor maps, it is critical to include every possible detail, meaning minor structures and local pile markers are clearly shown. To navigate safely from your final harbor approach right down to your assigned slip, charts such as harbor plans and berth diagrams are strictly required. Scales for these detailed sheets range from 25,001:1 down to 5,000:1.
● Highly detailed, including all local hazards, mooring buoys, and shore-side structures.
● Extremely useful at the very end of an approach or as a precision docking aid.
● These normally appear in regional chart books as small cutouts or inset panels alongside larger coastal maps.
Scales and errors
As well as showing the precise position of items on the water, a chart scale also dictates how much inherent mapping error is legally acceptable. While complex error calculations are outside the scope of this beginner guide, always maintain a safety buffer when plotting your course. Modern GPS navigation systems have highlighted this error factor because older paper maps may be slightly inaccurate regarding where physical objects sit on the earth.
If you draw a line on a paper chart with a sharp mechanical pencil, the graphite mark is about half a millimeter wide. Pixels on an electronic plotter are roughly 0.2mm wide, and the most accurate manual positioning on a printed page is about 0.3mm. Despite its thin visual appearance, a pencil line on a 1:1,000,000 general chart actually covers 500 meters of open water. By contrast, a single pixel covers an area of only one meter on a harbor chart scaled to 1:5,000.
Frequently Asked Questions
What are the main types of nautical charts?
Nautical charts are generally broken down into categories based on scale and use, including sailing charts, general charts, coastal charts, approach charts, and harbor charts.
Are paper charts still necessary if I have a GPS?
Yes. Electronic chart plotters are fantastic, but paper charts serve as an essential backup if you experience a total electrical failure or equipment malfunction onboard.
What does a small-scale nautical chart mean?
In cartography, a small scale means the map covers a large geographic area with less detail. These are used for ocean planning and long-distance passages.
How often should nautical charts be updated?
Charts should be updated regularly using official Notices to Mariners to ensure newly reported hazards, shifting shoals, and moved buoys are accounted for.
What is the difference between an ENC and an RNC?
An Electronic Navigational Chart (ENC) is vector-based data that allows interactive zooming and data customization, whereas a Raster Navigational Chart (RNC) is essentially a digital scan of a traditional paper chart.