Routing decisions for unclassified / unknown roads


I am having a slight issue with maps generated from regarding routing via
unknown roads.

On a Nuvi 2515, you wont be routed down one of these unless you are practically on the road. The system instead opts to route you via a much longer road.

Is this the logic that was put into the garmin map generation ?

Also what is the case for unclassified roads?

Where can I look for more information on this?



Oh, and routing is set to shortest path

“Unknown Roads” can be everything, so it’s correct behavior that routers use these roads with lowest priority.

Unclassified roads are normal roads comparable to residential roads. So, they should route similar to residential roads.

This can all be determined via the style-rule file for the mkgmap program which generates the gamin img files from
OSM data.

If you create your own maps with this program you can change everything.


Also check out this thread which is about the webpage:

Turns out this road is actually unclassified.

Is there anywhere I can get the style file used for this generation by Lambertus ? The alternate route is about six times as long. osrm does agree to
route via it but garmin does not.


I guess he uses the default style, but I suggest you ask him in the mentioned thread.

Can you post the osrm-Link (click on generate link) ?
So I can check if my nuvi is also showing this problem.

A possible reason could be a slightly missmoved node leading to a Z-shape, which the garmin
router does not like.


On routing works fine

routing from mpabana road to bombo road as on



Also I use the imgage at Generic Routable (testing new style)