clarify the sp() from table process

[mdsumner]

Example

library(choroplethrMaps)

data(state.map)
##?state.map
head(state.map)

## use spbabel to restore to sp
library(spbabel)

## we need to use particular naming conventions 

library(dplyr)
babel_table <- state.map %>% 
  mutate(island_ = !hole)  %>% 
  rename(object_ = id, x_ = long, y_ = lat, order_ = order, branch_ = group ) %>% 
  dplyr::select(-piece, -hole)

# library(ggplot2)
# ggplot(state.map, aes(long, lat, group=group, fill = group)) + 
#   geom_polygon() + guides(fill = FALSE)
# 
# ggplot(babel_table, aes(x_, y_, group=branch_, fill = branch_)) + 
#   geom_polygon() + guides(fill = FALSE)


## convert to sp
sp.state.map <- spbabel::sp(babel_table)
#sp.state.map <- spbabel::sp(babel_table, crs = "+init=epsg:4326")


## convert to sf
library(sf)
sf.state.map <- sf::st_as_sf(sp.state.map)
sf.state.map