code: function (coord, clamp) {
          var extent = this._extent;
          var scale = this.scale;
  
          if (this.onBand && scale.type === 'ordinal') {
              extent = extent.slice();
              fixExtentWithBands(extent, scale.count());
          }
  
          var t = linearMap(coord, extent, NORMALIZED_EXTENT, clamp);
  
          return this.scale.scale(t);
      }
docs: Convert coord to data. Data is the rank if it has an ordinal scale
  @param {number} coord
  @param  {boolean} clamp
  @return {number}