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I'm planning to enter concentrations of groundwater contaminants collected from well locations into QGIS and then use interpolation functions to create contours of the groundwater plume. Can QGIS calculate the maximum distance from a known point (e.g. a well) to an interpolated contour line (e.g. a contour line with concentration of 5 ppb)?

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It can definitely be done, but I know only one way — through one of the database plugins (and conversion to vector format). Eg. PostGIS' ST_MaxDistance could be used.

Interesting that you need the maximum! I hope you won't have problems with contours that intersect the bounding box, since you have limited data for the edges.

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And if you want to find that "far away point" you can use ST_LongestLine combined with ST_EndPoint –  Nicklas Avén Jun 19 '12 at 12:50
    
Thanks, I'll explore these options. @lynxlynxlynx, I suspect your right and the edge of my bounding box may cause some trouble. I'm interesting in the max distance from the source of contamination to the and edge of the contaminant plume (as define by select contours). That way I'll know how far the contamination has travelled. I have 100's of sites/plumes and I'd like to avoid manually measuring the distances. –  Patrick Jun 19 '12 at 21:40
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