openstreetmaps vs. Garmin CNNT maps

I have both North America CNNT maps (2015) and openstreetmaps (2015.7) installed on my Garmin Montana 600. one thing I noticed that there are many routing errors with OSM, while routing in Garmin is almost always superior than OSM routing, for example, if I want to calculate route from DC to downtown Los Angeles, OSM couldn’t find a valid route, and in my local area Washington DC metro area, OSM frequently gives doubtful route from point A to point B.

I heard some ppl have better luck with OSM in other parts of the world, I’m curious in which region/country OSM maps are more complete and reliable than Garmin maps.

I’m surprised to hear that. I would think that would be no problem for OSM. Are you sure your routing preferences are set properly? If, for example, you told Monty to avoid toll roads it will require a long and difficult route calculation.

Aside from that, I agree Garmin maps do handle routing pretty well in the U.S. The accuracy of OSM maps for any part of the world really depends upon how many mappers are working in the particular area you’re trying to route through. In Europe, where the OSM community is huge and dedicated, the OSM maps are quite excellent. Many states in the U.S. need mapping help as a large percentage of the coverage was derived from free but horribly inaccurate Tiger data from the U.S. government.

I live most of the year in northern Thailand and the OSM maps are much more accurate than Garmin maps. We have a small but dedicated group that does the heavy lifting and our work is very thorough. Other parts of Thailand are less good but still very useful.



Please try my maps of USA:

I have tried to improve a bit routing, but this is quite difficult task.

thanks, popej.

I downloaded the map over the weekend and tested on my Garmin device. it improved over previous version (USA OSM 2015.7), but the routing is still lacking. a 25 mile trip between home and work has directed me to unnecessary HOV lane change and wrong turns near destination (200 12th street s, Arlington 22202).

thanks though, I’ll still keep it as a city/hiking map instead of routing map.

Could you provide some example routes with comments? I can investigate and maybe invent some improvements.

here’s the route i took:

from lakeridge middle school (address:12350 Mohican Rd, Woodbridge, VA 22192) to arlington virginia (addr: 200 12th street s, Arlington 22202):

  1. i was directed to I-95 North bound highway correctly, then about 2/3 along the trip, after i switched to I-395 NB from I-95, i was directed to change to HOV (high occupancy vehicle) lane of I-395 near exit 3, this is unnessary since NB I-395 lanes are open, and HOV section of highway is time restricted and change directions based on the time of the day, fortunately at that time, the lane is open to North-bound traffic.

  2. near my destination, i got off the I-395 HOV lane and exit highway, should make a left turn onto Army-Navy drive but the GPS isn’t sure whether should turn left or right.

  3. at the end of Army-navy drive, after turning left onto south 12th streeet, my destination is just a couple hundred meters on the right, but i was told to turn right onto South Clark st.

Thanks for this example.

Mkgmap can’t create map with temporary restrictions, I guess I should make HOV undesirable for routing so main lanes would be taken as default. This is how route goes on BaseCamp anyway.

What does it mean?

On OSM this street is marked as one way, that’s why detour. I don’t know if one way is correct or not, you can edit OSM data if this is an error.

What does it mean?

what it means is that while i was on the short street leading to the Army-navy drive, gps first says making right turn, then immediately says turning left (which is correct).

the street allows two-way traffic, i’ll try to correct it in OSM.

Was it South Eads Street? I can imagine additional hint at first junction with Army Navy Street, but I don’t get it on BaseCamp. Maybe it depends on GPS, I don’t think I can correct it.

I encountered another strange occurrence with OSM routing.

yesterday I was visiting UMBC campus using ‘OSM South-Atlantic topo map’.

after the visit, I left the campus area via UMBC Boulevard, the GPS seems to ignore the nearby I-95 S entrance and directed me to MD-295 S a few kilometers down the same road.

starting point:
1000, Hilltop Circle, Paradise, Catonsville, Baltimore County, Maryland, 21228

end point:
12350 Mohican Rd, Woodbridge, VA 22192

device used:
Garmin Mobile XT 5.2 on Nokia E71

i’m not sure why the most obvious choice (I-95 in this case) was ignored and GPS picks another road (MD-295).