Projections: When using Clipper, Neighbor finder, Buffer etc., what Coordinate System is best for producing a result for distance in meters?

It all depends on the area you're working in really (and the use case) - I typically default to the relative UTM zone as that is fairly industry standard as far as I can tell.

One other thi​ng to check when choosing the coordinate system in FME is the units (feet vs degrees vs meters). In the US in particular you need to be a bit careful.

Others who are probably more expert in the area can probably provide a bit more insight. In general the question of "which projection is best?" Is not specific to FME.

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Thanks for the response! Good points.

This is for analysis in the US. Example would be extracting points that wall within a polygon and determining how far the outside points are from that polygon.

Very true, the projection is not a specific FME question.

Another way to do this is to use Dynamic Coordinate Systems in FME. I covered this in my weekly online stream here: https://www.youtube.com/watch?v=QB3LXE9ycp0&t=2007s

Basically, you reproject to a dynamic, equal area, coordinate system in order to take the measurements. Then you reproject back again. It's about the most accurate way of doing this because all features get the same origin point and so are less distorted than a regular reprojection.

Check out the video for more details. In fact, I like this question so much that I'm going to make it one of my questions-of-the-week.