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I am using qGIS v 1.7.4 for MAC and trying to calculate mean coordinates for a set of points using ftools.

To calculate my result I am going to Vector -> Analysis tools -> mean coordinates and then getting a plot output to a new layer.

However, the point seems to be totally off, even if I filter out outliers in my original points set.

Furthermore, I've read it's possible to calculate both regular and weighted means but don't find this option anywhere.

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It works for me on windows, so maybe the Mac version is bugged. Check you have the correct layer selected first (obvious I know but easy-done). For the weighted mean, choose your weight field from the drop-down menu just below where you select which layer you calculating the mean coordinate on. The option is labelled "Weight field". If you can't see that then you are definitely missing something and I suggest you install the latest version (1.9). –  MappaGnosis Jul 10 '12 at 7:12
    
For your "off" results, are you using the wrong projection for your project? i.e. for many tools you need to use UTM and set the layer to one of these types of projections. –  Willy Jul 10 '12 at 12:53
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