Why is my buffer an elipse?

Question

I've generated a simple 20 mile buffer on a point in Southern California but it comes out as an ellipse. When I use the measuring tool the buffer ring is 20 miles from the point, but shouldn't it be a circle? I'm using GCS North American 1983 for the coordinate system and the Datum is D North American 1983.

DanPatterson_Retired · Accepted Answer

Your buffer is an ellipse since it is in Geographic Coordinates.  If you want a circle, then set the map/dataframe to a projected coordinate system.  Longitude spacing decreases as you head poleward, so circles defined in geographic coordinates become ellipses.

Thanks to 'Tissot' this is a well documented phenomenon

Tissot's indicatrix helps illustrate map projection distortion

Tissot's indicatrix - Wikipedia