I have 60,000 points (denoting properties) in a raster and I'm trying to measure the distance from each one to a line (denoting the coastline). I've tried using Near and a couple of other tools like Spatial Join to measure the distance between each point and the line but each time it gives me ridiculous answers (when using planar as my method). When I used geodesic it gave answers that were closer to expected but still almost twice the accurate distance. I know this because using the 'measure' tool gives me the proper distance, but I cannot do that for 60,000 points (plus it does not give the shortest distance).
Both my layers are in different coordinate systems, which I understand could be causing this problem, but I don't know how to fix it. Whenever I try to change the coordinate systems to match up using Define Projection, I end up with the data being placed in ridiculous places. The line (coastline) data is in British National Grid (OSGB1936) and the points (properties) data is in WGS84.
Can someone tell me either how to measure the distance between them without having these issues or change the coordinate systems so I can finally measure the accurate distance between these points and the line?
Best Answer
To complement @Vince's comment you would typically use the define projection tool on a dataset that has no coordinate information. This is usually because what ever created the dataset in the first place was not really a GIS system so does not generate standard spatial datasets or it could be as simple as the person who sent you the data did not understand that some spatial datasets are a collection of files, the classic being a shapefile and they did not send you the
prjfile.If the data has a coordinate system then to convert it from one coordinate system into another you need to use the Project tool. So in your case you want to project the points into British National Grid so you can generate meaningful distances when you run the data through the Near tool. As with all projections you need to set a transformation, this is the equation used in the projection. This is a bit of a mine field but thankfully ArcGIS Pro defaults to the transformation with the best accuracy and that's WGS_1984_To_OSGB_1936_OSTN15, so use that.
You want to go from WGS84 to BNG as WGS84 is in units of decimal degrees, so I hope you agree that a distance of 300m is far more understandable than 0.00001 decimal degrees which actually changes with latitude.