Selects the projection of maps; this is ignored for vertical sections, time-lon and time-lat plots.

• The default depends on the daatset. Most often it is a lat-lon map, but for a few arctic and antarctic datasets it is a polar projection.
• Lat-lon: an equal distance latitude-longitude map (not a Mercator projection).
• North-polar stereograhic: equal distance in latitude, polar in longitude. Default the plot is cut off at 20°N.
• South-polar stereograhic: equal distance in latitude, polar in longitude. Default the plot is cut off at 20°S.
• Robinson: the oval IPCC style. Only works for longitude from 180°W to 180°E.