R language: how to plot shapefiles with open limits?

A dummy question I'm asking after trying to fix it by myself and googleing for a while. I need to plot several maps, which involve adding countries' limits. So far, I have used the following script:

rm(list = ls(all.names = TRUE))
library(raster)
library(geodata)

e <- extent(-76.5, -60.0, -3.0, 3.5)

paises <- c("BRA", "COL", "ECU", "VEN")
for(i in 1:length(paises)){
     if(i == 1){
          shps0 <- gadm(paises[i], level=0, path = tempdir(), version="latest", resolution=1)
     } else {
          temp <- gadm(paises[i], level=0, path = tempdir(), version="latest", resolution=1)
          shps0 <- rbind(temp, shps0)
     }
}
shps0 <- crop(shps0,e)

This yields the following map (without the colored arrows) of the region among Colombia, Brazil, Venezuela Ecuador, and Peru:

However, I would like to remove the artificial limits (black lines indicated by the red arrows) from the plot and display a continuous representation of the data, including the portions where the countries farther "continue" (indicated by the green arrows), something like this:

For just plotting and for this particular case it probably makes no difference, but mask() transforms SpatVector returned by gadm() to raster. Though you can keep vector shapes if you just transform polygons to lines first. With terra, which is loaded by geodata anyway, it might look something like this:

library(geodata)
#> Loading required package: terra
#> terra 1.7.23
library(terra)

shps0_poly <- gadm(c("BRA", "COL", "ECU", "VEN"), level = 0, path = tempdir())
shps0_poly
#>  class       : SpatVector 
#>  geometry    : polygons 
#>  dimensions  : 4, 2  (geometries, attributes)
#>  extent      : -92.00854, -28.84764, -33.74632, 15.91248  (xmin, xmax, ymin, ymax)
#>  coord. ref. : lon/lat WGS 84 (EPSG:4326) 
#>  names       : GID_0  COUNTRY
#>  type        : <chr>    <chr>
#>  values      :   BRA   Brazil
#>                  COL Colombia
#>                  ECU  Ecuador
as.data.frame(shps0_poly)
#>   GID_0   COUNTRY
#> 1   BRA    Brazil
#> 2   COL  Colombia
#> 3   ECU   Ecuador
#> 4   VEN Venezuela

shps0_lines <- as.lines(shps0_poly) |> 
  crop(ext(-76.5, -60.0, -3.0, 3.5))
shps0_lines
#>  class       : SpatVector 
#>  geometry    : lines 
#>  dimensions  : 4, 2  (geometries, attributes)
#>  extent      : -76.5, -63.37228, -3, 3.5  (xmin, xmax, ymin, ymax)
#>  coord. ref. : lon/lat WGS 84 (EPSG:4326) 
#>  names       : GID_0  COUNTRY
#>  type        : <chr>    <chr>
#>  values      :   BRA   Brazil
#>                  COL Colombia
#>                  ECU  Ecuador
as.data.frame(shps0_lines)
#>   GID_0   COUNTRY
#> 1   BRA    Brazil
#> 2   COL  Colombia
#> 3   ECU   Ecuador
#> 4   VEN Venezuela

plot(shps0_lines)

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^{Created on 2023-04-19 with reprex v2.0.2}

You are not using the current version of terra. So the first thing to do is to update that package. The issue you are having that the axes of the plot follow the canvas size, not the map size. In the current version of "terra" that is not the case.

library(geodata)
library(terra)
pols <- gadm(c("BRA", "COL", "ECU", "VEN"), level = 0, path = tempdir())
e <- ext(-76.5, -60.0, -3.0, 3.5)

If you just wanted to add these polygons as lines on top of an existing plot (map), say or raster x that I create below, you can do

x <- rast(e, vals=1)
plot(x)
lines(pols)

If you want to start by plotting lines you could do

plot(e, border=NA)
lines(pols)

You can also do

plot(pols, xlim=c(-76.5, -60.0), ylim=c(-3.0, 3.5), axes=FALSE)
plot(pols, ext=c(-76.5, -60.0, -3.0, 3.5), axes=FALSE)

That is, you do not need to crop the polygons. If you do, @margusl solution to use as.lines(pols) is fine, but it should not be necessary.

Well, problem fixed: I must use mask instead of crop... thanks anyway