It is better, but next time please try to make a complete self-contained reproducible example (as explained in the guide).
I think your problem is the use of merge() try with left_join() instead, see this reprex
library(tidyverse)
library(ggmap)
states <- map_data("state")
AEP <- data.frame(Impressions = c(9434L, 10060L, 5686L, 22694L, 5998L),
region = as.factor(c("alabama", "arizona", "arkansas", "california",
"colorado")))
mapdata <- states %>%
left_join(AEP, by="region")
ggplot(data = mapdata) +
geom_polygon(mapping = aes(x=long,y=lat,group=group, fill=Impressions))
