The 'TopologyException: Input geom 1 is invalid' self-intersection error which arises from invalid polygon geometries has been widely discussed. However, I haven't found a convenient solution on the web that solely relies on R functionality.

For instance, I have managed to create a 'SpatialPolygons' object from the output of map("state", ...) following Josh O'Brien's nice answer here.


map_states = map("state", fill = TRUE, plot = FALSE)

IDs = sapply(strsplit(map_states$names, ":"), "[[", 1)
spydf_states = map2SpatialPolygons(map_states, IDs = IDs, proj4string = CRS("+init=epsg:4326"))



The problem with this widely applied dataset is now that self-intersection occurs at the point given below.

Warning message:
In RGEOSUnaryPredFunc(spgeom, byid, "rgeos_isvalid") :
  Self-intersection at or near point -122.22023214285259 38.060546477866055

Unfortunately, this problem prevents any further use of 'spydf_states', e.g. when calling rgeos::gIntersection. How can I solve this issue from within R?

  • 1
    If you zoom in around that point: plot(spydf_states, xlim=c(-122.1,-122.3),ylim=c(38,38.1)) you'll see there's no "seemingly" about it - there's a self-intersection.
    – Spacedman
    Commented Sep 18, 2015 at 15:27

1 Answer 1


Using a zero-width buffer cleans up many topology problems in R.

spydf_states <- gBuffer(spydf_states, byid=TRUE, width=0)

However working with unprojected lat-long coordinates can cause rgeos to throw warnings.

Here's an extended example that reprojects to an Albers projection first:



# many geos functions require projections and you're probably going to end
# up plotting this eventually so we convert it to albers before cleaning up
# the polygons since you should use that if you are plotting the US
spydf_states <- spTransform(spydf_states, 
                            CRS("+proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=37.5 +lon_0=-96"))

# simplify the polgons a tad (tweak 0.00001 to your liking)
spydf_states <- gSimplify(spydf_states, tol = 0.00001)

# this is a well known R / GEOS hack (usually combined with the above) to 
# deal with "bad" polygons
spydf_states <- gBuffer(spydf_states, byid=TRUE, width=0)

# any bad polys?
sum(gIsValid(spydf_states, byid=TRUE)==FALSE)

## [1] 0


enter image description here

  • 7
    any extra commentary/reading on why the gBuffer "hack" works? Commented Nov 8, 2016 at 1:10
  • do you want to use gSimplify as it tears down the data.frame and converts the SPDF into spatial polygon object?
    – wnursal
    Commented Nov 14, 2016 at 6:31
  • 20
    If you're using sf you can also use sf::st_buffer(x, dist = 0)
    – Phil
    Commented Jan 8, 2019 at 9:27
  • 1
    also works in some case when using PostGIS
    – natsuapo
    Commented Aug 21, 2019 at 7:42
  • 7
    In sf there is a function st_is_valid(spydf_states) and a st_make_valid(spydf_states). I tried them and they work great. Commented Apr 28, 2021 at 23:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.