Coastal charts have scales ranging from approximately 1:50,000 to 1:150,000, as defined by their intended use for inshore navigation. This means that for every 1 unit of measurement on the chart, the actual distance on the earth is 50,000 to 150,000 units respectively.
Understanding Coastal Chart Scales
Coastal charts are specifically designed for navigating in areas where the course might lie within outlying reefs and shoals. They also assist in entering or leaving bays and harbors of considerable width and navigating large inland waterways. The scales of these charts are selected to balance the need for detailed representation with the manageability of the chart itself.
Key Features Influenced by Scale:
- Detail Level: At the larger end of the scale range (e.g., 1:50,000), more detail is shown than at the smaller end (e.g., 1:150,000). This means that features such as small channels, rocks, and depth contours are more clearly defined.
- Coverage Area: A chart with a scale of 1:50,000 will cover a smaller geographic area than a chart with a scale of 1:150,000. The smaller the scale, the larger the area depicted on a single chart.
- Navigation Use: Coastal charts bridge the gap between larger scale harbor charts, which show specific port details, and smaller scale general charts that cover entire coastlines. They are tailored for general coastal navigation while still offering useful detail for local maneuvering.
Table of Common Chart Scales:
| Chart Type | Scale Range | Intended Use |
|---|---|---|
| Harbor Charts | 1:2,000 to 1:50,000 | Detailed port layouts, anchoring areas, and berthing details |
| Coastal Charts | 1:50,000 to 1:150,000 | Inshore coastwise navigation, entering bays/harbors, and navigating large inland waterways. |
| General Charts | 1:150,000 to 1:5,000,000 | Overall coastline views, planning longer voyages |
| Oceanic (Sailing) Charts | 1:5,000,000 or smaller | Transoceanic navigation |
This understanding of scale is crucial for navigators to accurately plan their routes and execute safe passage through coastal waters. It allows for the appropriate balance between detailed information and overall coverage.
