code: def markers(data, marker, f_tooltip=None, marker_preferred_size=32):
      
      from geoplotlib.layers import MarkersLayer
      _global_config.layers.append(MarkersLayer(data, marker, f_tooltip, marker_preferred_size))
docs: Draw markers
  
      :param data: data access object
      :param marker: full filename of the marker image
      :param f_tooltip: function to generate a tooltip on mouseover
      :param marker_preferred_size: size in pixel for the marker images