Improve select area visuals

Improve the aesthetics of plotting select_area. Eg remove boundaries of neighbouring regions (if desired)

Below, is an example of the current output. It is preferable to only plot the borders of the region you are interested in, or have the choice whether or not these other borders are shown.

A possible solution may be to select only the select_area in the regions object within the function (and drop the other areas).

首先定位实现 select_area 的绘图函数，并检查 regions 对象的使用方式。重现示例输出，然后验证在选定区域仍保持绘制的情况下，是否可以省略或控制相邻区域的边界。