This is an abstract superclass. A coverage describes some geographic phenomenon distributed over an arbitrary region of space.
The most distinguishing aspect of a coverage is that it has a spatial function. A spatial function is a function defined on positions in space. It can be used to model: either continuous phenomena or discrete phenomena. Input to the function is a spatial object. Output from the function is unrestricted. The function may be very simple, such as an assignment of image values to grid positions in the case of a raster. Alternatively, the function may be sophisticated, involving for example the interpolation of values at arbitrary locations.
SAIF does not provide direct support for methods or functions. Nevertheless, coverage types can be described in SAIF by emphasizing the structural aspects of the data. Thus the spatial function is interpreted in SAIF as a simple assignment of thematic or topographic values to specific positions within a given region.