Just download the zip, unpack it and then run the following code
require("rgdal")
require("sp")
#read path to shapefile
shapefile_path=readline("Path to Shali shapefile: ")
#import shapefile
wrld_brdrs=readOGR(shapefile_path)
#select countries
slct=c('Senegal', 'Guinea', 'Guinea-Bissau',
'Sierra Leone', 'Mali', 'Niger',
'Chad', 'Sudan', 'Eritrea', 'Ethiopia', 'Benin', 'Burkina Faso',
'Togo', 'Ghana', 'Nigeria', 'Cameroon', 'Gambia', 'Liberia', 'Mauritania',"Cote d'Ivoire")
slct_areas=wrld_brdrs[wrld_brdrs$NAME==slct[1] | wrld_brdrs$NAME==slct[2] | wrld_brdrs$NAME==slct[3] |
wrld_brdrs$NAME==slct[4] | wrld_brdrs$NAME==slct[5] | wrld_brdrs$NAME==slct[6] |
wrld_brdrs$NAME==slct[7] | wrld_brdrs$NAME==slct[8] | wrld_brdrs$NAME==slct[9] |
wrld_brdrs$NAME==slct[10] | wrld_brdrs$NAME==slct[11] | wrld_brdrs$NAME==slct[12] |
wrld_brdrs$NAME==slct[13] | wrld_brdrs$NAME==slct[14] | wrld_brdrs$NAME==slct[15] |
wrld_brdrs$NAME==slct[16] | wrld_brdrs$NAME==slct[17] | wrld_brdrs$NAME==slct[18] |
wrld_brdrs$NAME==slct[19] | wrld_brdrs$NAME==slct[20],]
#Like this
plot(wrld_brdrs, bg="light blue")
plot(slct_areas, col=rainbow(n=21),add=T)
#OR like this?
plot(slct_areas,col=rainbow(n=21), bg="light blue")
plot(wrld_brdrs,add=T)
#OR like this
plot(africa, bg="light blue")
plot(slct_areas, col=rainbow(n=21),add=T)
#plus labels on the map
plot(africa, bg="light blue")
map.text("world", regions = slct, add=T)
plot(slct_areas, col=rainbow(n=21),add=T)
Plot 1:

Plot 2:

Plot 3:
