What Does a GPS Display When You Travel Beyond Mapping Coverage?

On my nuvi, I have California, Oregon, Canada and Mexico on my SD card. So to test this, I pulled the card and attempted to drive to Los Angeles, starting from the Arizona border. I couldn't. It refused to pull up Los Angeles at all.

Setting a trip to Seattle from the same point resulted in the nuvi ignoring Calfornia and Oregon completely and taking me through Nevada and Idaho to get to Washington.

So, in answer to your question, if the only map detail is the basemap, the nuvi ignores the base map in its calculations. This is not wholly unexpected, because you can't use a GPS with just a base map. The GPS will complain.

You can test this yourself. Just go into the settings and turn off the detailed map. The gps will then revert to the nonroutable base map.

The Flat Earth Society
"Deprogramming the masses since 1547"

Mission Statement
For centuries, mankind knew all there was to know about the shape of the Earth. It was a flat planet, shaped roughly like a circle, with lots of pointy things hanging down from the underside. On the comparatively smooth topside, Europe sat in the middle of the circle, with the other continents scattered about the fringes, and parts of Africa hanging over the edge. The oceans lapped against the sides of the Earth, and in places ran over, creating currents that would pull over the edge ships that ventured too far out to sea. The space beyond the edge of the world was a dark realm inhabited by all sorts of unholy beasts. Fire and brimstone billowed up from the very depths of hell itself and curled 'round the cliffs whose infinite length jutted straight down to the darkest depths . . . .

Then, in the year of our Lord fourteen-hundred and ninety-two, it all changed. For decades a small band of self-proclaimed "enlightened" individuals had been spouting their heretical nonsense that the Earth was in fact round. Citing "proof" based on nothing more than assumptions, half-truths and blind guesses, they dazzled the populace with their " . . . undeniable mathematical and scientific evidence . . . that the world is shaped not like a pancake, but an orange!"

Rightly wishing to dispel notions regarding the alleged citrus-like shape of our planet, the Church was able to either silence or execute nearly all the fanatics. But a small handful remained, continuing to spread their blasphemous speeches and to promote their heretical ideals involving the very center of the universe. One of their number, who called himself Grigori Efimovich, would later be known to the rest of the world as Christopher Columbus. Using an elaborate setup involving hundreds of mirrors and a few burlap sacks, he was able to create an illusion so convincing that it was actually believed he had sailed around the entire planet and landed in the West Indies. As we now know, he did not. What Efimovich actually did was sail across the Atlantic Ocean to a previously undiscovered continent, North America, and even then only to a small island off the coast. It took him several years more even to "discover" his blunder and claim it as a " . . . new world". But the damage had already been done, and mankind entered into what we now call its "Dark Ages" . . . .

If you can't map it...then it doesnt exist.
Turn around and go home.

Perhaps you could just put your GPS in simulation mode and set your coordinates outside your map area with "set location". This may give you what you want.

I have a 265WT. I zoomed out until I could see all of North America. I then dragged the screen until I was in the area of Germany. I zoomed in and there were roads and cities showing. Apparently there is a base map that covers the entire world.

Using my 255W, I set the unit to simulate mode, put in coordinates for London England, set new location to those coordinates, looked for “nearby cities” and picked Canvey, then did a simulated drive to that city. (My detail map is CN North America NT 2010.30)

So apparently one can create and use an internal route using the base map on the 255W

Took my Nuvi 200W to Vancouver (no Canada map coverage) and it simply showed the blue screen. However, I still liked having it as I figured that if something happened, just having the LAT/LON to report to emergency services was better than nothing.