mcenter LON LAT                       Set the map center

   Set the longitude (LON) and latitude (LAT) of the center of the map.

   The coordinate system used is either that of the projection (PCS),

   the data (DCS), the overlay grid (GCS), or is in cartesian pseudo-

   angles.  The choice is made by setting one of these through the

   command MCTYPE.

   The last coordinate system option (UV) is included to simplify

   interaction with image files (which have their own projection and

   map centers).  A zoomed-in portion of such an image is centered on

   a point that is a simple linear offset from the image map center.

   Using this system makes it easy to specify the region of interest

   for overlaying such a portion of an image.

