参考 [www.cnblogs.com](http://www.cnblogs.com/JoAnnal/p/6776916.html)

```{r}
library(maps)
data("world.cities")
```

```{r}
world.cities %>% 
    filter(country.etc == 'China',name == 'Shanghai')
```

直接学习了。

```{r}
bigcities <- subset(world.cities, pop > 5000000)
qplot(long, lat, data = bigcities,colour=country.etc,size=pop)+ borders("world", size= 0.5)
```
