你能改变ggplot2图形从正方形到矩形的比例吗？

I'm using geom_segment to plot a timeline of activity. It's all on the same line, and since I want to present it together with other graphs, I'd much rather make the y axis much smaller. It seems that the size of the gray graph area in ggplot2 is always square though, whether I scale it larger or smaller. Is there a way to say that I want x=500 y=50 or something like that? to plot a timeline of ac