What is "spatial feature encoding"? Can anyone give a concrete example?
Chatfield et al. provides a good survey of feature encoding methods. 

From the introduction to that paper (emphasis my own):


  The typical object recognition pipeline is composed of the following three steps: (i) extraction of local image features (e.g., SIFT descriptors), (ii) encoding of the local features in an image descriptor (e.g., a histogram of the quantized local features), and (iii) classification of the image descriptor (e.g., by a support vector machine).


I believe that "spatial feature encoding" refers to step (ii) in the typical pipeline. In this respect, I believe that the simplest possible example (and a standard one) would be the histogram encoding. If "spatial feature encoding" is meant to imply the preservation of some geometric information, than spatial binning is another technique to look at.