I am trying to create a soil-type map of an area from point data using QGIS. I tried interpolating the data, since soil is continuous. I did this by allocating a number to each point type and then using the interpolation function. I later created contours from the output file to delineate the areas. The problem that I am having is that the results from the interpolation and contours do not line up with the point data. The point data and contours are in close proximity to each other but do not overlay accurately.
I would like the output to be as if though I manually drew lines that connected and delineate the different types of soils/point data. Now the points lie outside of the delineated area. Is there another technique to do this or what am I doing wrong?
I used the Raster Interpolation Plugin in QGIS Wien. The interpolation method was IDW, Number of columns =300, Number of rows =300, Cellsize X = 0.00004, Cellsize Y =0.00006