Hi Ricky,
The original freesurfer surface has over a 100k vertices and are
decimated when setting up the source space for calculating the
lead-field and the MNE. Its described in section 3.5 of the MNE manual
version 2.7. When this decimation is done topology of a recursively
subdivided icosahedron by a factor of 5, one ends up with 10242 sources
per hemisphere.
The stc files have the original vertex number information in them. The
easiest way to make a label from an stc file is to view it on mne_analyze
and draw it using a mouse (see section 7.13.4 of the manual). Alternately
you could read the stc file into MATLAB using mne_read_stc_file() and work
with it. Freesurfer's write_label() MATLAB function would then be useful.
Regards,
Hari