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I am trying to create interpolated maps within geographical borders.

I have the coordinates and values to the points I am trying to interpolate. I also have a map of the geographical land mass in .shp file, within which I am trying to confine the interpolation.

Using GRASS in QGIS, I have managed to interpolate my points with v.surf.idw. But I seem unable to confine them to the map of my geographical region (Northern Quebec, bordering James and Hudson Bay), meaning that my gradient goes into the bay!

How do overlay my interpolation within the boundaries of Quebec?

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you can clip the interpolated raster with your border shapefile. Would that work? – spatialthoughts Jun 1 '12 at 6:49

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you may firt to change boundry to rast use commond v.to.rast then you can use r.mask make a mask, last fresh the display window,you will get the result.

i think the below result is what you want . enter image description here

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Thank you W. Hou, This actually helps! It gave me what I wanted! – Michel Jun 1 '12 at 18:26

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