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I have KML file from downloaded https://data.gov.sg/dataset/electoral-boundary_2020. As you can see on the website, there are 31 sub-polygons and each of them has a label. I have loaded the KML on R.

I have a separate .csv data file with postal codes, latitude and longitude. I would like to extract the name of the polygons from the KML file to map to the .csv to give 4 columns:

postal_code latitude longitude Name

Where Name is the name the polygon if the postal_code fall within the polygon. How do I do this using R?

Here is a sample data

library(rgdal)
library(spatialEco)
library(dplyr)

postal_code=c(117606, 640215, 600220, 628389, 118560, 267314, 129580, 268458)
latitude=c(1.283146, 1.348578, 1.340993, 1.303928, 1.277510, 1.321747, 1.315483, 1.322019)
longitude=c(103.7739, 103.7121, 103.7374, 103.6586, 103.7893, 103.7999, 103.7650, 103.7910)
df=cbind.data.frame(postal_code, latitude, longitude)

coordinates(df)<-~longitude+latitude

poly.sg=readOGR('Downloads/doc.kml', "ELD2020")
proj4string(poly.sg)
poly.sg=spTransform(poly.sg, CRS('+init=epsg:4326'))

I have tried to follow the steps in Join spatial point data to polygons in R

poly.sg2<-as(poly.sg, "SpatialPolygonsDataFrame")
pts.poly<-point.in.poly(df, poly.sg2)

I received this error

Error in st_geos_binop("intersects", x, y, sparse = sparse, prepared = prepared,  : st_crs(x) == st_crs(y) is not TRUE
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  • Have you seen this article gis.stackexchange.com/questions/137621/…? – Taras Oct 23 '20 at 6:51
  • @Taras Thank you for sharing the link. I have attempted to follow the steps in the link but encountered an error. – tatami Oct 23 '20 at 8:12
  • What kind of error? – MarcM Oct 23 '20 at 8:50
  • @MarcM it is in my question – tatami Oct 23 '20 at 13:25
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You are not setting the CRS to the df object; if you print it you'll notice

class       : SpatialPointsDataFrame 
features    : 8 
extent      : 103.6586, 103.7999, 1.27751, 1.348578  (xmin, xmax, ymin, ymax)
crs         : NA 

That crs is NA; so you have to set it:

library(raster) # for its Spatial*DataFrame print method
library(sp)
#...
coordinates(df)<-~longitude+latitude
sp::proj4string(df) = sp::CRS('+init=epsg:4326')

Then, when you print the df object again, you'll see:

class       : SpatialPointsDataFrame 
features    : 8 
extent      : 103.6586, 103.7999, 1.27751, 1.348578  (xmin, xmax, ymin, ymax)
crs         : +init=epsg:4326 +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +tow

Now your intersection should work

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  • Is crs() in crs(df) from the package raster? – tatami Oct 25 '20 at 16:30
  • yes, raster::crs(); I've edited the code; also, the object print in the code is from raster package – Elio Diaz Oct 25 '20 at 17:03
  • spatialEco imports sp and raster so both proj4strings and crs methods should be available – Elio Diaz Oct 25 '20 at 18:41

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