I want to do some spatial statistic analysis with the county-level crop yield data in Nebraska for the STAT class. For that I need the longitude and latitude of the geographic centroids of each county. Anybody know how to do it in R? I know it can be done in ArcGIS but I have no access to it now.
You didn't give any details where you got your shapefile from, but I got one from here and you can use gCentroid from rgeos thusly:
library(rgdal)
library(sp)
library(rgeos)
nebraska <- readOGR("CountyBoundsUTM/", "CountyUTM")
gCentroid(nebraska, byid=TRUE)
## SpatialPoints:
## x y
## 0 721768.5 4636738
## 1 430938.8 4524651
## 2 698036.4 4566570
## 3 370970.6 4641340
## ...
## 89 623301.6 4603228
## 90 618883.0 4486931
## 91 439295.3 4582756
## 92 493680.8 4522680
## Coordinate Reference System (CRS) arguments: +proj=utm +zone=14 +datum=NAD83
## +units=m +no_defs +ellps=GRS80 +towgs84=0,0,0