title: Drawing gridlines in cartopy map
body: <p>I am drawing the map above using cartopy and the foll. code:</p>
  
  <pre><code>gl = ax.gridlines(crs=ccrs.PlateCarree(), draw_labels=True, alpha=0.35)
  gl.xlabels_top = False
  gl.ylabels_left = False
  gl.xlocator = mticker.FixedLocator([-120, -60, 0, 60, 120])
  gl.xformatter = LONGITUDE_FORMATTER
  gl.yformatter = LATITUDE_FORMATTER
  </code></pre>
  
  <p>How do I restrict this to only draw gridlines for -23.5 N, 0 and 23.5 degree N latitude?</p>