[R-sig-Geo] Combine two polygons

[Roger Bivand]

Briefly, is sf::aggregate() what you are looking for? Or terra::aggregate() if you read with terra::vect()?

---
Roger Bivand
Emeritus Professor
Department of Economics
Norwegian School of Economics, Bergen, Norway

________________________________
Fra: Miluji Sb <milujisb using gmail.com>
Sendt: fredag 28. april 2023, 14:18
Til: Roger Bivand <Roger.Bivand using nhh.no>
Kopi: Michael Sumner <mdsumner using gmail.com>; R-sig-geo mailing list <r-sig-geo using r-project.org>
Emne: Re: [R-sig-Geo] Combine two polygons

Thank you for your replies. I think I am misunderstanding something. I have read the shapefile using sf. I would like to combine polygons for Cyprus and Northern Cyprus only within the world shapefile and keep all the other polygons as they are.

world <- sf::st_read(dsn = "~/gadm36_levels_shp", layer = "gadm36_0")

Is something like the following correct? I was thinking of generating a group variable which is unique to all the countries except Cyprus and Northern Cyprus. I a probably making this too complicated.

world %>%
  group_by(group) %>%
  summarise(geometry = sf::st_union(geometry)) %>%
  ungroup()

Thank you again.

Best regards,

Milu

On Fri, Apr 28, 2023 at 8:56 AM Roger Bivand <Roger.Bivand using nhh.no<mailto:Roger.Bivand using nhh.no>> wrote:
On Fri, 28 Apr 2023, Michael Sumner wrote:

> fwiw, a method with geodata/terra
>
> cyp <- geodata::gadm(country = c("CYP", "XNC"), path = tempdir(), version =
> "3.6")
>
> terra::aggregate(cyp)
>

and as per
https://github.com/r-spatial/evolution/blob/main/pkgapi_230305_refs.csv.

> see ?terra::writeVector to write it out
>
> (rgdal is very old and you should abandon it, it will be removed from
> support by the end of this year)

Thank you! Yes, sp will by default switch to using sf in place of rgdal
for creating "CRS" objects, and under sp::spTransform in June, and all
three retiring packages rgdal, rgeos, and maptools will be gone by October
2023. An sp release will appear in May with a transition guide.

It seems that terra does not have an object corresponding to sp's "CRS" or
sf's "crs". As far as I can see, one needs to create an empty
SpatVector/SpatRaster object and assign a CRS, coerce to "Spatial", and
extract its slot. If this makes sense, sp could use terra (and
raster, needed for coercion) rather than sf where workflows did not
otherwise use sf. Very grateful for input here or
https://github.com/r-spatial/evolution/issues.

Roger

>
>
> (just as an aside, we can't hit the geodata vector urls directly with gdal
> as we can with the rasters, as they are in an R specific format)
>
> Cheers, Mike
>
>
> On Fri, Apr 28, 2023 at 10:52 AM Ben Tupper <btupper using bigelow.org<mailto:btupper using bigelow.org>> wrote:
>
>> Hi,
>>
>> You might try st_union() from the sf package
>> https://r-spatial.github.io/sf/articles/sf3.html#geometrical-operations
>>
>>
>>
>> On Thu, Apr 27, 2023 at 5:37 PM Miluji Sb <milujisb using gmail.com<mailto:milujisb using gmail.com>> wrote:
>>
>>> Dear all,
>>>
>>> I am using the country-level shapefile from GADM. I would like to merge
>>> Cyprus and North Cyprus into one polygon. Is this possible? I am using
>>> rgdal to read the shapefile, subset, and then rewrite it. Any help will
>> be
>>> highly appreciated.
>>>
>>> ##
>>> world <- readOGR("~/gadm36_levels_shp", layer = "gadm36_0")
>>>
>>> Best regards,
>>>
>>> Milu
>>>
>>>         [[alternative HTML version deleted]]
>>>
>>> _______________________________________________
>>> R-sig-Geo mailing list
>>> R-sig-Geo using r-project.org<mailto:R-sig-Geo using r-project.org>
>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>
>>
>>         [[alternative HTML version deleted]]
>>
>> _______________________________________________
>> R-sig-Geo mailing list
>> R-sig-Geo using r-project.org<mailto:R-sig-Geo using r-project.org>
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>
>
>
>

--
Roger Bivand
Emeritus Professor
Department of Economics, Norwegian School of Economics,
Postboks 3490 Ytre Sandviken, 5045 Bergen, Norway.
e-mail: Roger.Bivand using nhh.no<mailto:Roger.Bivand using nhh.no>
https://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en_______________________________________________
R-sig-Geo mailing list
R-sig-Geo using r-project.org<mailto:R-sig-Geo using r-project.org>
https://stat.ethz.ch/mailman/listinfo/r-sig-geo


	[[alternative HTML version deleted]]