I would like to calculate a buffer of 5km around country polygons. However, I somehow always get a warning and an error. Here is a reproducible example code.

countries_sp <- ne_countries(scale = 10)

countries_sp <- countries_sp[(countries_sp@data$geounit %in% "France"), ]

proj4string(countries_sp) <- CRS("+init=epsg:4326") 

countries_for_buff <- st_as_sf(countries_sp, crs ="+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m +no_defs ")

countries_buff_5km <- st_buffer( countries_for_buff, 5000)

here the warning:

dist is assumed to be in decimal degrees (arc_degrees).
Warning message:
In st_buffer.sfc(st_geometry(x), dist, nQuadSegs, endCapStyle = endCapStyle,  :
st_buffer does not correctly buffer longitude/latitude data


tm_shape(countries_sp) +
  tm_polygons() +
tm_shape(countries_buff_5km) +

gives the error

 Error in if (all(tiny) && show.messages) warning("all relative area sizes are below thres.poly",  : 
   missing value where TRUE/FALSE needed

What am I doing wrong? I guess there is something about the projection that does not quite work out the way it should.

  • Which query language? – jlSta Feb 8 '19 at 11:51
  • The language is R, sorry – S Front Feb 8 '19 at 11:53

This is unnecessary because the object is already in that coordinate system:

proj4string(countries_sp) <- CRS("+init=epsg:4326") 

This doesn't do a coordinate transformation - the crs argument is ignored - what made you think it did something?

countries_for_buff <- st_as_sf(countries_sp, crs ="+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m +no_defs ")

If you don't believe its ignored, try:

> countries_for_buff <- st_as_sf(countries_sp, crs ="bogus")

So then when you do:

countries_buff_5km <- st_buffer( countries_for_buff, 5000)

then countries_for_buff is still in lat-long coordinates.

To convert from one to another you need either spTransform for sp objects or st_transform for sf objects.

so something like this on the sp object:

  csp2 = spTransform(countries_sp,"+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m +no_defs ")
  • 1
    great thank you! Because the plotting st_buffer does not accept sp objects, I used st_as_sf and the warning let me believe that something about the projection was wrong so I just simply tried some other projections – S Front Feb 8 '19 at 12:07
  • If you want to buffer sp objects then use gBuffer from the rgeos package. But sf objects are mostly better and I'd advise converting to sf as early as possible. – Spacedman Feb 8 '19 at 16:04

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