The graphic type is a reference to an instance of an HLU object. The file type is a reference to a file in a supported file format. The logical type is generated from relational expressions. Logical values are either True or False . Graphic values are returned by the create statement, HLU functions or the getvalues statement, and file values are returned by the addfile intrinsic function.
Coercion is basically the implicit conversion of data from one data type to another.
This occurs when two values of different types are operands to the same operator. Operands must be of a compatible type to perform the requested operation. For example, when a float value is multiplied by an integer value, the integer value can easily, without losing or corrupting the value, be converted to a float value. Because there is no loss of information, NCL does this automatically. The following table lists the automatic conversion possibilities for all of the basic types.