[R-sig-Geo] extracting centroids from map data

[Bede-Fazekas Ákos]

Hello Andy,
you'll need these:

library(rgeos)
centroids <- gCentroid(states, byid=TRUE, id = NULL)

after you convert your data.frame to SpatialPolygons or 
SpatialPolygonsDataFrame (package sp).
HTH,
Ákos

2016.05.20. 5:41 keltezéssel, Andy Bunn írta:
> Hello all, I'm working on a map. I'd like to extract centroids of the counties below in order to plot them as points. How can I do this?
>
> Many thanks, Andy
>
> ~~~~
>
> library(ggplot2)
> library(maps)
> all_states <- map_data("county")
> states <- subset(all_states, region %in% c("iowa",  "illinois", "indiana",
>                                             "michigan", "minnesota","ohio",
>                                             "wisconsin"))
> p <- ggplot()
> p <- p + geom_polygon( data=states, aes(x=long, y=lat, group = group),
>                         color="grey10", fill="white" )
> p <- p + theme(aspect.ratio=1)
> p
>
>
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