require(raster)
require(sp)
require(gdal)

setwd("C:/Users/XXX/Desktop/data"

polys <- readOGR(dsn=get_wd(), layer = "world_shapefile"
raster.a <- raster(raster_a.txt)
raster.b <- raster(raster_b.txt)

plot(polys)
plot(raster.a)
plot(raster.b)