A user supplied function to transform the coordinate longitudes and latitudes to a plot coordinate system. By using this transform, we can change from a longitude, latitude coordinate to a polar stereographic project, for example. Initially, x[0]..[n-1] are the longitudes and y[0]..y[n-1] are the corresponding latitudes. After the call to mapform(), x[] and y[] should be replaced by the corresponding plot coordinates. If no transform is desired, mapform can be replaced by NULL.

The interval in degrees at which the longitude lines are to be plotted.

The interval in degrees at which the latitude lines are to be plotted.

The value of the longitude on the left side of the plot. The value of minlong must be less than the value of maxlong, and the quantity maxlong-minlong must be less than or equal to 360.

The value of the longitude on the right side of the plot.

The minimum latitude to be plotted on the background. One can always use -90.0 as the boundary outside the plot window will be automatically eliminated. However, the program will be faster if one can reduce the size of the background plotted.

The maximum latitudes to be plotted on the background. One can always use 90.0 as the boundary outside the plot window will be automatically eliminated.