Adjusts the given array-coordinate to the scrolling; this means that coordinates east/west of
the east/west map-edge are converted to the corresponding coordinate on the map.
Every subclass of this class implements all data and function that is specific to the particular
type of map (at present flat or iso) QuadMap runs on at the moment.
A rectangle, defined by the top-left and the bottom-right-corner (inclusive)
The top-left-corner must always have smaller/equal x and y-coords
than the bottom-right-one.
A Ruleset object normally maps to one *.ruleset file, from which
it builds its data collection by way of a Parser object invoked by
a Registry instance.
If this FieldView stores some images (and doesn't just load and
calculate the needed images inside the paint-method), this
method recalculates that images.