ggplot(sm.df, aes(year, N, group = 1)) + geom_line(aes(colour = top10)) +
facet_wrap( ~ shortTitle, ncol=7) +
theme_bw() +
theme(panel.grid.major = element_blank(),
panel.grid.minor = element_blank(),
axis.text.x = element_text(angle=45, hjust=1, size =8)) +
scale_x_discrete(breaks=seq(1989, 2020, 8)) +
ylim(0, 150)

'data.frame':   78 obs. of  3 variables:
 $ x1     : num  12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 ...
 $ y1     : num  130 130 130 130 130 130 130 130 130 130 ...
 $ N.label: int  1650 1456 1348 1216 1086 1035 985 940 888 826 ...