CODEWITHSUNDEEP
r
Ekow_ababio
Ekow_ababio

Reputation: 163

Convert a column value(s) in SpatialpolygonDataframe into raster image

I need help with converting a variable or column values in a spatial polygon into a raster image. I have spatial data of administrative units with income(mean) information for each unit. I want to convert this information into raster for further analysis.

I tried the code below but it didn't work.

r <- raster(ncol=5,nrow=15) 
r.inc <- rasterize(DK,r,field=DK@data[,2],fun=mean)

Where SP is the spatial polygon and the mean income for each spatial unit stored in column 2 of the SpatialPolygonDataframe. Can anyone help with a function or code of how to rasterise the values in the column of interest? An example of the spatialpolygondataframe (created) and my attempt to rasterize the data are below

suppressPackageStartupMessages(library(tidyverse))
url = "https://api.dataforsyningen.dk/landsdele?format=geojson"
geofile = tempfile()
download.file(url, geofile)
DK <- rgdal::readOGR(geofile)
DK@data = subset(DK@data, select = c(navn))
DK@data$inc = runif(11, min=5000, max=80000)
require(raster)
r <- raster(ncol=5,nrow=15) 
r.inc <- rasterize(DK,r,field=DK@data[,2],fun=mean)
plot(r.inc)

Thank you.

Acknowledgement: The code for creating the sample SPDF was sourced from Mikkel Freltoft Krogsholm (link below).

https://www.linkedin.com/pulse/easy-maps-denmark-r-mikkel-freltoft-krogsholm/?trk=read_related_article-card_title

Upvotes: 0

Views: 117

Answers (1)

Andrew Chisholm
Andrew Chisholm

Reputation: 6567

Here's something that makes a raster.

library(tidyverse)
library(rgdal)
library(raster)
url <- "https://api.dataforsyningen.dk/landsdele?format=geojson"
geofile <- tempfile()
download.file(url, geofile)
DK <- rgdal::readOGR(geofile)
r_dk <- raster(DK, nrows = 100, ncols = 100)      # Make a raster of the same size as the spatial polygon with many cells
DK$inc <- runif(nrow(DK), min=5000, max=80000)    # Add some fake income data
rr <- rasterize(DK, r_dk, field='inc')            # Rasterize the polygon into the raster - fun = 'mean' won't make any difference
                                                                                             
plot(rr)

enter image description here

The original raster was the size of the whole Earth so I think Denmark was being averaged to nothing. I resolved this by making an empty raster based on the extent of the DK spatial polygons with 100x100 cells. I also simplified the code. Generally, if you find yourself using @ with spatial data manipulation, it's a sign that there might be a simpler way. Because the resolution of the raster is much larger than the size of each DK region, taking the average doesn't make much difference.

Upvotes: 1

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