rules for garmin maps

Is there a list somewhere that documents the undocumented rules, pitfalls and hidden traps in making maps for Garmin?
Something I recently tripped over and spent a lot of time trying to figure out was where I had a map built that looked as expected on qmapshack, but some of the roads did not show up as expected on my Garmin Montana. I would change the element type for a way, but it wouldn’t show up as expected on the garmin. The problem was that I had another map on the garmin that I had built that was on the device, and it seems like the TYP data from that one was being used instead of my new one.

The other item I don’t understand is the various names. I don’t use mapsource or sendmap, I use qmapshack and use the OS to copy maps to the device.
The various names don’t show up on the Garmin. The --description shows up as the map name on the Montana. There is a 2nd map name line shown for some maps which I didn’t build which I’d like to use if I could figure out how.

Does family ID have to be unique, ie not conflicting with other maps on the device? This may be related to my issue above?

This website is a bit out of date but it contains lots of tips & tricks that are still valid:
http://www.cferrero.net/maps/maps_index.html
The family ID has to be unique. Please check it with various tools from Javawa (https://www.javawa.nl/) another great source for the map maker.

Yes, thx, I’ve been using that one. Everything seems a bit out of date, or incomplete.

The mkgmap mailing list (http://www.mkgmap.org.uk/pipermail/mkgmap-dev/2018q4/thread.html) is the goto place for this sort of thing (but often the traffic is about highly detailed rules by very experienced users).

I think in general fewer people are relying on making Garmin maps now that good maps are available on phones, so there has been less interest in updating the information.

I don’t think FID is the key. I have 2 maps with different FID that don’t show up in the garmin map list and 2 with the same FID (Openfietsmap) that do show up.
My OS is linux, so many of those tools don’t work, bu from GMapTool there is a cmd line tool,
Here’s the output for the 2 maps, where only 1 shows up.

gmt v0.8.220.853b  CC BY-SA (C) 2011-2015 AP www.gmaptool.eu
File:		cco.img, length 2247680
Header:   	02.12.2018 19:47:31, DSKIMG, XOR 00, V 1.00, Ms 0
Mapset:   	cco

Map              length s-f  CP    prio  PID   FID  name
 MAKEGMAP MPS        73  1
 00030001 IDX     30388  2
 00TYP001 TYP     34814  1  1252           1 30001
 63240001 MPC   2167991  5  1252  20       1 30001  cco
Data MPS
 F: PID 1, FID 30001, famname
 V: OSM map set (0)
 
gmt v0.8.220.853b  CC BY-SA (C) 2011-2015 AP www.gmaptool.eu
File:		colo_brh.img, length 103055360
Header:   	02.12.2018 20:45:50, DSKIMG, XOR 00, V 1.00, Ms 0
Mapset:   	colo_brh

Map              length s-f  CP    prio  PID   FID  name
 MAKEGMAP MPS       895  1
 00088085 IDX   1727218  2
 TYP88085 TYP     34818  1  1252           1 22549
 63240001 MPC   4168028  5  1252  20       1 22549  colo_brh
 63240002 MPC   4935553  5  1252  20       1 22549  colo_brh
 63240003 MPC   8529883  5  1252  20       1 22549  colo_brh
 63240004 MPC   5051897  5  1252  20       1 22549  colo_brh
 63240005 MPC   5085767  5  1252  20       1 22549  colo_brh
 63240006 MPC   5010055  5  1252  20       1 22549  colo_brh
 63240007 MPC   3542464  5  1252  20       1 22549  colo_brh
 63240008 MPC   8220812  5  1252  20       1 22549  colo_brh
 63240009 MPC   4914466  5  1252  20       1 22549  colo_brh
 63240010 MPC   5355294  5  1252  20       1 22549  colo_brh
 63240011 MPC   9445514  5  1252  20       1 22549  colo_brh
 63240012 MPC   7509685  5  1252  20       1 22549  colo_brh
 63240013 MPC   7852702  5  1252  20       1 22549  colo_brh
 63240014 MPC   5336651  5  1252  20       1 22549  colo_brh
 63240015 MPC   9466203  5  1252  20       1 22549  colo_brh
 63240016 MPC   6650265  5  1252  20       1 22549  colo_brh

Data MPS
 F: PID 1, FID 22549, OSM map
 V: OSM map set (0)

I’ve been bothering the mkgmap-dev list with other questions, so I thought I try here 1st.