绘制二维密度散点图，根据x，y的最大最小值将坐标分成若干小格，然后统计落在每个小格里的点数，最后形成的就是一个矩阵，然后直接出图-Drawing two-dimensional density scatter plot, according to the x, y minimum and maximum values ​ ​ of the coordinates into a number of small cells, then every little statistic falls Gerry points, the final form is a matrix, and then direct the map