Testing turf.buffer accuracy

I am getting a rather large difference comparing turf.buffer to the result of a buffer generated in GIS software. The GIS buffer was projected in MD state plane, then queried to a geoJson feature using SR 4326 via esri’s REST api. Using a leaflet measure tool to ground truth, the GIS buffer was accurate. Does anyone have a good explanation?

var point = turf.point([-76.675801, 38.935749]);
var buffered = turf.buffer(point, 10, {units: 'miles'});

[SteveCline]

Thanks @rowanwins

I think passing a spatial reference code as an option would be very helpful for the buffer and probably some other methods too. I would argue, if turf’s philosophy is to ‘just work as expected’, using proper spatial reference is vitally important to that expectation of working.

Mid latitude buffers will be off by 25% and running turf.circle will give a more accurate result in these parts of the globe.

If turf has the goal of being the geoprocessing engine of the future, which I hope it does, it can’t have inaccuracies this large and be used in serious GIS applications. Thanks again for your help and good work with Turf!

[chrispahm]

@SteveCline @JamesLMilner Trying to help clean up some older issues here: Similar to issues #1470, #1484, #1547 this issue has been fixed with Turf >v6.2.0.

Here’s a small notebook showcasing Turf’s buffer operation on the point and 10 mile buffer radius presented in @SteveCline’s original question for both Turf v6.5.0 and v5.1.6. The buffer is compared to a buffer calculated using GeoPandas (link to Jupyter notebook used for the calculation.

https://observablehq.com/@chrispahm/turf-issue-1246

Since the difference is arguably small, I guess this issue can be closed as well!