我正在try 创建一个美国的choropleth map ，默认 colored颜色 从灰色变为白色.
我有48个州中的18个州的记录，代码按值着色，但对于那些我没有记录的州，状态是灰色的.我希望它们是白色的.
我该如何改变 colored颜色 ？
library(maps)
library(plyr)
library(ggplot2)
records1<-read.csv('E:/My Documents/records_by_state.csv')
records<-data.frame(state=tolower(rownames(records1)), records1)
head(records)
all_states<-map_data("state")
head(all_states)
record_map<-merge(all_states, records, by.x="region", by.y="state.name")
record_map<-arrange(record_map, group, order)
head(record_map)
p<- ggplot()
p<- p + geom_polygon(data=record_map, aes(x=long, y=lat, group=group, fill=record_map$Records), colour="black"
)+ scale_fill_continuous(low="thistle2", high="darkred", guide="colorbar")
P1 <- p + theme_bw() +labs(fill= "Records by State"
, title= "By State", x="", y="")
P1 + scale_y_continuous(breaks=c()) + scale_x_continuous(breaks=c()) + theme(panel.border= element_blank())