function getLayerType(geoFeatureDef) {
  return geoFeatureDef.pair ? LAYER_TYPES.heatmap : LAYER_TYPES.hexagonId;
}
@param {Array<Object>} geoFeatures geo feature definitions, contains {name, pair}. geoFeatures.pair is an array of 2 geo feature definitions representing lat, lng columns of that feature
@returns {String} layer type field of kepler config