This layer replaces master2000 for the previous datum NAD27.  The mastertic tics were recreated with new tic ids that are based on a hashing of their state plane coordinates.  The idtics are unique within the last 4 digits for a vicinity of 100,000 feet square.  The idtics will be the same for tics at the same location between the two tic sets (so tics don't double up when appended).  (For example, a tic with xtic = 2,480,000 and ytic = 360,000 will have a tic id of 02346800 at any of the tic intervals 2000, 5000, 10,000, and 20,000.)  Other tic sets have been created that can be moved into covers that follow the same rules for tic ids: master10k, master20k, master50k, master100k, quadtic2_5m, quadtic5m, quadtic7_5m, quadtic10m, quadtic15m, and quadtic30m.  The quadtic covers have hashed tic ids based on the geographic coordinate intervals that are used on USGS 7.5, 15, and 30 minute quads