I have a vector layer with incidence data (i.e. frequencies) and I made a graded color map from this using the above frequencies. Now I am looking forward to creating an interpolated (kriging) map from the above frequencies. Is there a method to create such interpolated map from my incidence data? (or else is it possible to create a interpolated map with out a point layer?) Thanks.
Based on the comments, it sounds like @Jakob found an appropriate solution. The polygon layer needs to first be converted to centroid points. This is done using:
Vector -> Geometry Tools -> Polygon Centroid
and then creating the output point layer. The interpolation may then be performed using one of the various methods available. This post has a good discussion of interpolation in QGIS.