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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

Taras
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tatami
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  • Have you seen this article https://gis.stackexchange.com/questions/137621/join-spatial-point-data-to-polygons-in-r? – Taras Oct 23 '20 at 06:51
  • @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 08:12
  • What kind of error? – MarcM Oct 23 '20 at 08:50
  • @MarcM it is in my question – tatami Oct 23 '20 at 13:25
  • Without seeing what is being imported from readOGR I can only speculate but, you do not need to coerce to an sp class as, it is already there. Meaning, the polg.sg2 object is not necessary. Besides, the point.in.poly function handles both sp and sf objects. – Jeffrey Evans Dec 25 '21 at 19:28

1 Answers1

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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

Elio Diaz
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