ggmap在地图上用圆圈可视化数据

I am trying to create a map that shows in circles the cities where subjects in my data set originated. I would like the circles to be proportional to the number of people in the city in my data. I would also like an additional circle to be a subset of the original circle showing the people in each city afflicted by the disease.I am trying to create a map that shows in circl