symbolSize (symbolSize) {
        if (!arguments.length) {
            return this._symbolSize;
        }
        this._symbolSize = symbolSize;
        return this;
    }
Set or get radius for symbols.
@see {@link https://github.com/d3/d3-shape/blob/master/README.md#symbol_size d3.symbol.size}
@param {Number} [symbolSize=3]
@returns {Number|ScatterPlot}