2

OK so I have a spatial polygons data frame, and I have a point of interest. I want to add a row to the SPDF that contains the distance from the centroid of each polygon to this given point. How do I do this ?

Here is a toy dataset:

    library(sp)
    library(spdep)
    library(rgeos)

    # Create toy SPDF
    fn <- system.file("etc/shapes/eire.shp", package = "spdep")[1]
    prj <- CRS("+proj=utm +zone=30 +units=km")
    eire <- readShapeSpatial(fn, ID = "names", proj4string = prj)

    # Create a point of interest
    pt.coords <-readWKT("POINT(260 5900)")
    eire.proj<-CRS(proj4string(eire))
    proj4string(pt.coords) <- eire.proj

    # check point is on the map
    plot(eire)
    plot(pt.coords, col="Red", add=TRUE)

Ok so the SPDF data has following columns:

    > names(eire)
   [1] "A"       "towns"   "pale"    "size"    "ROADACC" "OWNCONS" "POPCHG"  "RETSALE" "INCOME"  "names"  

I want to add a extra column showing the distance from each polygon centroid to the point we defined. How do I do this ?

3

ok figured it out eventually myself

    centroid.ED <-SpatialPoints(coordinates(eire))
    proj4string(centroid.ED) <- eire.proj
    eire$distance <- gDistance(pt.coords,centroid.ED,byid=TRUE)

    > summary(eire$distance)
           1         
     Min.   : 18.44  
     1st Qu.: 56.78  
     Median : 99.48  
     Mean   :106.46  
     3rd Qu.:156.60  
     Max.   :223.84  

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