Coordinate system for shapefile, no .prj file, using R

Question

I am trying to use the shapefiles found on this page for oil & gas data from the Netherlands: https://www.nlog.nl/en/files-interactive-map from table at the bottom with "ARC_grid" and "Google Earth (WGS84)" columns and icons.

Specifically the "Oil and gas fields" ARC_grid files (https://www.nlog.nl/sites/default/files/nlog_velden_ed_1950_utm_31n_20170829.zip)

I am using R to download, read and plot the shapefile. I am able to do this OK, but the shapefile does not seem to have a coordinate reference system, I believe due to the absence of the .prj file.

The coordinates I get when I read the file in look like this:

 [1,] 683985.7 5931987
 [2,] 684138.5 5931975

I would like them in Lat/Long, but do not know how to find out what conversion to use initially.

I am looking for an R-based solution.

Using R, this is how I have loaded the file:

temp <- tempfile(fileext = ".zip")
download.file("https://www.nlog.nl/sites/default/files/nlog_velden_ed_1950_utm_31n_20170829.zip", destfile = temp)
filepaths <- unzip(temp)

map <- readOGR(".")

map@proj4string
# CRS arguments: NA

Answer 1

Go to projfinder, type in one of your coordinate points and zoom the map to where you think the point should be:

http://projfinder.com/

projfinder will then try lots of coordinate systems and for the ones that map onto your map it will list them.

you then need to use your knowledge to figure out which one its most likely to be. In this case WGS84 UTM zone 31N unless its old data that might have used a previous geodetic reference like WGS 72 - but they're pretty close together.

Answer 2

From a quick look, most other datasets on the website have a specific PRJ file - perhaps that particular one just wasn't copied over properly. I'd try copying one from a related dataset, put it in the same directory as the shapefile you need and rename it to: nlog_velden_ed_1950_utm_31n_20170829.prj.

Then you can reproject as needed in ArcGIS. I'd double check to make sure everything seems right, but I'd bet that would do it.

Answer 3

The data appear to be projected in UTM Zone 31N, given the naming convention of the files and the coordinate values. That makes sense, as that UTM zone covers the western half of the Netherlands.