CODEWITHSUNDEEP
rspatialshapefile
Adrian V
Adrian V

Reputation: 21

Finding the shared border of two shapefiles in order to measure the shortest distance of a spatial point to the border

I have shapefiles on two states that border each other, I need to isolate the shared border of the two states, and then calculate the distance to the border for a bunch of points. I can't just define one point on the border and measure the distance to that, I need to have each point scan for the closest point on the border, while the border info I have is in shapefile form.

Any suggestions? I dropped a picture in if it helps visualize the problem.

Here is a picture

Upvotes: 0

Views: 560

Answers (1)

nniloc
nniloc

Reputation: 4243

To answer the first part of your question, you can convert the polygons to lines of the perimeters, then sf::st_intersection to find the overlap of the two perimeters.

For the second part of your question, consider breaking the overlap line into 100 or 1000 points using st_sample, then finding the distance between those points and the points within the state polygon using st_nearest_feature. See here for more details: https://gis.stackexchange.com/a/288575/162034

library(sf)
#> Linking to GEOS 3.9.0, GDAL 3.2.1, PROJ 7.2.1

# Get state data
us_states <- st_as_sf(maps:::map("state", plot = FALSE, fill = TRUE))
states2 <- subset(us_states, ID %in% c("new jersey", "pennsylvania"))

# Convert polygons to lines
states2_perim <- st_cast(states2, "MULTILINESTRING")

# Find overlap of lines
states2_overlap <- st_intersection(states2_perim)
#> although coordinates are longitude/latitude, st_intersection assumes that they are planar

# Plot
plot(st_geometry(states2))
plot(st_geometry(subset(states2_overlap, n.overlaps == 2)), col = 'red', lwd = 2, add = TRUE)

Created on 2022-02-14 by the reprex package (v2.0.0)

Upvotes: 1

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