r - Error: ggplot2 doesn't know how to deal with data of class SpatialPointsDataFrame -

i trying follow tutorial found on http://www.r-bloggers.com/mapping-the-worlds-biggest-airlines/. able plot following tutorial, convert robinson projection. have noticed there might error ne_10m_populated_places.shp after doing readogr command. please me figure out must spatial shapes?

library(ggplot2) library(maps) library(rgeos) library(maptools) gpclibpermit() library(rgdal)  worldmapin<- readshapepoly("ne_10m_admin_0_countries.shp") worldmap_ogr <- readogr(".", "ne_10m_admin_0_countries") worldrobinson <- sptransform(worldmap_ogr, crs("+proj=robin +lon_0=0 +x_0=0 +y_0=0 +ellps=wgs84 +datum=wgs84 +units=m +no_defs"))  urbanareasin<- readshapepoly("ne_10m_urban_areas.shp") urbanareas_ogr <- readogr(".", "ne_10m_urban_areas") urbanareasrobinson <- sptransform(urbanareas_ogr, crs("+proj=robin +lon_0=0 +x_0=0 +y_0=0 +ellps=wgs84 +datum=wgs84 +units=m +no_defs")) simp<- gsimplify(urbanareasrobinson, 10, topologypreserve=t) urbanareas<-fortify(simp)  placesin<- readshapespatial("ne_10m_populated_places") placesin_ogr <- readogr(".", "ne_10m_populated_places") placesinrobinson <- sptransform(placesin_ogr, crs("+proj=robin +lon_0=0 +x_0=0 +y_0=0 +ellps=wgs84 +datum=wgs84 +units=m +no_defs"))  base<- ggplot(worldmapin) wrld<-c(geom_polygon(aes(long,lat,group=group), size = 0.1, colour= "#090d2a", fill="#ffffff", alpha=1, data=worldmap))urb<- c(geom_polygon(aes(long,lat,group=group), size = 0.1, colour= "#fcfff1", fill="#fcfff1", alpha=1, data=urbanareas)) places<-geom_text(data=placesinrobinson, aes(longitude, latitude, label = name), size=1)  base+wrld+urb+places