function usa_shape_display ( lon, lat, filename, plot_title )

%*****************************************************************************80
%
%% USA_SHAPE_DISPLAY displays a shape defined by longitudes and latitudes.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    04 November 2016
%
%  Parameters:
%
%    Input, real LON(*), LAT(*), the longitude and latitude of the points.
%
%    Input, string FILENAME, a name for the graphics file.
%    If FILENAME is '', the plot is not saved.
%
%    Input, string PLOT_TITLE, a title for the plot.
%
  fprintf ( 1, '\n' );
  fprintf ( 1, 'USA_SHAPE_DISPLAY:\n' );
  fprintf ( 1, '  MATLAB version\n' );
  fprintf ( 1, '  Display the shape of a region defined by longitudes and latitudes.\n' );
%
%  Open a new graphics figure.
%
  figure

  plot ( lon, lat, 'r-', 'Markersize', 15 );
  axis ( 'equal' );
  grid ( 'on' );
  xlabel ( 'Longitude' );
  ylabel ( 'Latitude' );
  title ( plot_title );
%
%  If FILENAME is not empty, save a copy of the plot.
%
  if ( ~ isempty ( filename ) )
    fprintf ( 1, '\n' );
    fprintf ( 1, '  Plot saved as "%s"\n', filename );
    print ( '-dpng', filename )
  end

  return
end
