Currently, the map has a 7.6km/pixel (4.7mile) pixel resolution, at the Equator, with approx. 7% of the derived source file(s) size.
Timezones are plotted from the shapefile found at The World Timezone Shapefile Repository
Those files have subsequently been modified with "quasi-maritime" timezones and unique colors are assigned indexing the polygons.
For those timezones at sea, quick and dirty 15 degree polygons were unceremoniously added. The 24 new polygons were added to the 418 pre-existing named polygons. Although
uninhabited isn't an official timezone, the entire list of timezones (443) was assigned a colour in 35 point increments.
Current logic looks to 8 points (0-315) around the compass to see if there is a 'land' timezone within 12 nautical miles, otherwise it becomes 'International' plus or minus the appropriate hour UTC.
When it's all over except the shouting,
timmeh might be able to ask if you want/need to change your timezome/locale, or if confidence is high, make those changes automagically.
sudo -H pip3 install gps3 will install gps3 with a fast delivery from the Cheese Shop
Grab your machine and fire up your gps, make sure it all works.
timmeh.py and the image(s) you want to test in the same directory and
python3 timmeh.py away on your favourite terminal, multiple times a day if you're adventurous like me.