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

Question

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

Please post a fully reproducible example including data. This will increase the chances of getting an answer. — Andrew Chisholm
– Andrew Chisholm, Commented Jun 4, 2021 at 13:03
thank Andrew, I've edited the question to include sample data and my code. — Ekow_ababio
– Ekow_ababio, Commented Jun 4, 2021 at 19:30

Andrew Chisholm · Accepted Answer · 2021-06-04 21:42:40Z

1

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)

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.

edited Jun 4, 2021 at 21:42

answered Jun 4, 2021 at 21:30

Andrew Chisholm

6,5972 gold badges26 silver badges43 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Ekow_ababio Over a year ago

Thanks, Andrew. Also, thank you so the insightful explanation.

Collectives™ on Stack Overflow

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

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related