Function mapOpacityChart

mapOpacityChart(json?): void
Set the nautical chart layer opacity.

Setting this value to zero hides the nautical chart layer. Setting this value to one shows the layer at full opacity.
Parameters
- json: {
  opacity: number;
  } = ...
  - opacity: number
    number: 0 to 1
Returns void
Example
```
{opacity: 0.6}
```