Where can I find a good resource that teaches me
1) about the difference between proj4, EPSG and ESRI *.prj? (Why do several coordinate system definitions exist? When should I use which? How are they defined?)
2) how the conversion between these systems works in detail.
I came across these questions while encountering a problem with EPSG 2056 which I defined using the proj4 string (I wrongly assumed that the EPSG is an ID for the proj4 string). When exporting this coordinate system to a shapefile using the function st_write from the R package sf I realized that the ESRI *.prj file did not translate correctly. I assume it has something to do with the towgs84 paramter which ESRI does not recognize.