Hi.

That 167ft tolerance should be a more or less constant offset for a large area (such as a minor city (by american standards) or at least a few square kilometers, and only little different for the next part of a map. They say that the position is in degres with 6 significant digits, so this would be about 11cm (4") of tolerance between neighbouring landmarks (like streets or buildings). This is pretty good. I am just wondering how fast the offset (that is up to 167ft) might change.
However: My major point was that it would be difficult to correctly locate the current position on the map if the software doesn't already know the current offset (at least almost correctly, like within 1m or 2m/3ft or 6ft). In my case, my home is in a street that is a dead end, but within 167ft there are two parallel streets that both aren't dead ends. So if the software was assuming the wrong street, it would give totally incorrect instructions. I was just saying that the software would need some interface that allows for easy adjustment of the current offset.
Citymaps and RoutePlanner are using a very simple approach: You tell the software that you want to adjust the offset now, and it displays the part of the map that contains the current position (without correction). You can then move that map around and/or search for a street and finally just click on the position that you think is correct. The software than simply applies the offset you thereby entered to any following operation.
IWBN if the software was automatically compensating changes in the offset by snapping to the street you are currently driving along.

cu,
sven