Map of ireland code taken from https://gist.github.com/halhen/659780120accd82e043986c8b57deae0 and data from http://ec.europa.eu/eurostat/web/gisco/geodata/reference-data/population-distribution-demography/geostat

france

France
filter(lng > 32, lng < 44) %>%
    filter(lat > 22, lat < 31) %>%
Italy
+     filter(lng > 40, lng < 51) %>%
+     filter(lat > 14.7, lat < 26) %>%
Germany
    filter(lng > 40, lng < 48) %>%
    filter(lat > 26, lat < 36) %>%

MapIreland

 read_csv('GEOSTAT_grid_POP_1K_2011_V2_0_1.csv') %>%
    rbind(read_csv('JRC-GHSL_AIT-grid-POP_1K_2011.csv') %>%
              mutate(TOT_P_CON_DT='')) %>%
    mutate(lat = as.numeric(gsub('.*N([0-9]+)[EW].*', '\\1', GRD_ID))/100,
           lng = as.numeric(gsub('.*[EW]([0-9]+)', '\\1', GRD_ID)) * ifelse(gsub('.*([EW]).*', '\\1', GRD_ID) == 'W', -1, 1) / 100) %>%
    filter(lng > 28, lng < 34) %>%
    filter(lat > 28, lat < 34) %>%
    group_by(lng=round(lng, 1), lat=round(lat, 1)) %>%
    summarize(value = sum(TOT_P, na.rm=TRUE))  %>%
    ungroup() %>%
    group_by(lat) %>%
    arrange(lng) %>%
    mutate(next.value = lead(value)) %>%
    ggplot(aes(lng, lat + 5*(value/max(value)), xend=lng+0.1, yend=lat + 5*(next.value/max(value)))) +
    geom_segment(size=0.4, alpha=0.8, color='#5A3E37') +
    ggthemes::theme_map() +
    coord_equal(0.9)

uk.r

read_csv('GEOSTAT_grid_POP_1K_2011_V2_0_1.csv') %>%
    rbind(read_csv('JRC-GHSL_AIT-grid-POP_1K_2011.csv') %>%
              mutate(TOT_P_CON_DT='')) %>%
    mutate(lat = as.numeric(gsub('.*N([0-9]+)[EW].*', '\\1', GRD_ID))/100,
           lng = as.numeric(gsub('.*[EW]([0-9]+)', '\\1', GRD_ID)) * ifelse(gsub('.*([EW]).*', '\\1', GRD_ID) == 'W', -1, 1) / 100) %>%
    filter(lng > 29, lng < 38) %>%
    filter(lat > 30, lat < 42) %>%
    group_by(lng=round(lng, 1), lat=round(lat, 1)) %>%
    summarize(value = sum(TOT_P, na.rm=TRUE))  %>%
    ungroup() %>%
    group_by(lat) %>%
    arrange(lng) %>%
    mutate(next.value = lead(value)) %>%
    ggplot(aes(lng, lat + 5*(value/max(value)), xend=lng+0.1, yend=lat + 5*(next.value/max(value)))) +
    geom_segment(size=0.4, alpha=0.9, color='#5A3E37') +
    ggthemes::theme_map() +
    coord_equal(0.9)