问题
I use to plot maps of Belgium available on GADM (select Belgium) using R.
I import and plot the outside boundary of Belgium using :
belgium <-readRDS("gadm36_BEL_0_sp.rds")
plot(belgium)
Which gives me :
I import and plot the boundaries of provinces of Belgium using :
provinces <-readRDS("gadm36_BEL_2_sp.rds")
plot(provinces)
Which gives me :
What i'm trying to have is a dataframe with boundaries of provinces that are NOT outside boundaries of Belgium :
I tried using over(), intersect(), etc but did not founded yet a method to do that. Several approach can be used I guess :
- substract belgium boundary to the province dataset;
- Work only in the provinces dataset and keep only commons boundaries;
- else?
Thanks if you have a solution. Grégoire
回答1:
I downloaded the sf formatted files from that site (https://www.gadm.org/download_country_v3.html), since the sf package is a bit easier to deal with.
library(dplyr)
library(sf)
provinces <- readRDS("gadm36_BEL_2_sf.rds")
interiors <- st_intersection(provinces) %>%
filter(n.overlaps > 1)
interiors
# Number of columns truncated for clarity:
# interiors %>% select(VARNAME_2, geometry, n.overlaps)
Simple feature collection with 30 features and 2 fields geometry type: GEOMETRY dimension: XY bbox: xmin: 2.851679 ymin: 49.8004 xmax: 6.033082 ymax: 51.35568 epsg (SRID): 4326 proj4string: +proj=longlat +datum=WGS84 +no_defs First 10 features: VARNAME_2 1 Amberes|Antuérpia|Antwerp|Anvers|Anversa 2 Amberes|Antuérpia|Antwerp|Anvers|Anversa 3 Brussel Hoofstadt|Brusselse Hoofdstedelijke Gewest|Brüssel|Bruxelas|Région de Bruxelles-Capitale|Brussels|Bruselas 4 Limbourg|Limburgo 5 Flandres Oriental|Fiandra Orientale|Flandes Oriental|Flandre orientale|East Flanders|Ost Flandern 6 Amberes|Antuérpia|Antwerp|Anvers|Anversa 7 Amberes|Antuérpia|Antwerp|Anvers|Anversa 8 Amberes|Antuérpia|Antwerp|Anvers|Anversa 9 Flandres Oriental|Fiandra Orientale|Flandes Oriental|Flandre orientale|East Flanders|Ost Flandern 10 Brabant Flamand|Brabante Flamenco|Brabante Flamengo|Flemish Brabant n.overlaps geometry 1 2 MULTILINESTRING ((5.239571 ... 2 2 MULTILINESTRING ((4.327078 ... 3 2 MULTILINESTRING ((4.403365 ... 4 2 MULTILINESTRING ((5.117446 ... 5 2 MULTILINESTRING ((4.243931 ... 6 3 POINT (4.994605 51.0414) 7 3 POINT (4.243931 51.04332) 8 2 MULTILINESTRING ((4.994605 ... 9 2 MULTILINESTRING ((3.466959 ... 10 2 MULTILINESTRING ((5.025736 ...
To check with a plot:
plot(interiors$geometry)
What you're doing here is looking for the spatial intersection of the provinces with every other province. Then you filter out the intersections where it's just a province overlapping itself (n.overlaps == 1). That way you only get the interior borders where one or more provinces touches another (n.overlaps > 1), but not any province alone (which would be an external border).
This is an updated version of this excellent answer: https://stackoverflow.com/a/47761959/3330437
To remove the circled points (intersections of 3 provinces) in the map and dataset, you can use:
interiors %>% filter(!st_is(., "POINT"))
来源：https://stackoverflow.com/questions/57137126/compare-spatial-polygons-and-keep-or-delete-common-boundaries-in-r