*Reasons may include
- Continuation of coverage of a small part outside the main area of chart coverage e.g a river.
- Inset plans and the chart title block and notes also take up space, therefore geographical information cannot be shown in this area.
- A need to refer to larger scale of chart, such waters are often "blued out" to avoid excessive maintenance work applying numerous NM corrections to an area of the small scale chart where the navigator will be using a larger scale chart.
- Coverage is better served from a different chart because of typical routeings.