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I'm working in QGIS. I have a multipolygon layer and I want to create a 1.5 mile buffer around the outer edge of each polygon.

The output of the Buffer tool (set to 1.5 miles) doesn't quite reach 1.5 miles.

Why is this? Is the Buffer tool somehow calculating 1.5 miles from a center point in the polygon?

I want the result to be 1.5 miles from all outer edges of the polygon.

See current result below. Buffer extends only 1.12 miles from outer edge of polygon.

enter image description here

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    What projection is your data in? Did you check eliposidal?
    – Ian Turton ♦
    Commented Apr 9 at 19:06
  • Make sure that you measure the length in the same projection as the layer projection, and that the same projection was set when you used the Buffer tool. The projection must be in meters (miles), not degrees.
    – Comrade Che
    Commented Apr 10 at 4:22
  • @IanTurton Thanks. Yes, eliposidal was checked and when I check cartesian, it measures to 1.5 miles. Why is that? What is the difference between the too?
    – csft306
    Commented Apr 10 at 22:07
  • Elipsoidal accounts for the curvature of the Earth while Cartesian assumes it is flat, if your projected buffer matches the cartesian measure then your are using a projected CRS?
    – Ian Turton ♦
    Commented Apr 11 at 7:39
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    Never ever use 3857 for geographic analysis - it distorts the further north or south you go
    – Ian Turton ♦
    Commented Apr 11 at 17:30

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