readOGR加載shape文件時報錯

加載shape文件時報錯：
> library(rgdal)
> maps <- readOGR(dsn="/srv/shiny-server/fortune500-master",
+                 layer = "ne_50m_admin_1_states_provinces_lakes", 
+                  encoding = "UTF-8",verbose=FALSE)
Error in ogrInfo(dsn = dsn, layer = layer, encoding = encoding, use_iconv = use_iconv,  : 
  Cannot open file
  
解決辦法：
相關目錄缺少下面的文件
ne_50m_admin_1_states_provinces_lakes.shp
ne_50m_admin_1_states_provinces_lakes.dbf
ne_50m_admin_1_states_provinces_lakes.shx
注意：只有shp文件也會報錯，dbf,shx文件也不能少
在下面的地址下載：
http://peteraldhous.com/Data/storms/ne_50m_admin_1_states_provinces_lakes/


readOGR的用法參考：
http://facweb.knowlton.ohio-state.edu/pviton/courses2/crp87105/spatial-data.html