You cannot trust maps. Even those maps that would seem to come from the most reliable sources are often wrong. In argumentation, the Appeal to Authority is fallacious as to whether or not a proposition is true. The same could be said for geographic information. When it comes to maps, there are no absolute authorities.
I have personally caught numerous egregious errors on publicly available maps printed by both Government and Private organizations. With almost any map, if you are aware of the ground truth of a region, you can usually spot an honest error in toponym location or spelling. Errors of geographic location are a little more rare, but satisfying to spot. The best errors to find are those where the cartographer has created an imaginary place that doesn't even exist on the ground. Today I'll point out a funny error from an organization that you would typically apply "authority" to. But, that would be a mistake.
Imagine you wanted to find a town in Montana and how to get there. You could use Google or Bing, but probably you would prefer a map from those who maintain and catalog the roads themselves: The Montana Department of Transportation. I in no way mean to slight the MDT. They work hard and do a wonderful job, despite constant bitching from the populace regarding snowplows, road conditions, and construction. The road miles per capita for Montana is significant, the country and weather rough, and the miles traveled per person far. They couldn't do it without Federal money.
Any way, say you and your wife wanted to take a trip from Helena, Montana to Corbin, Montana. Maybe you want to check out The Alta, one of Montana's great historic silver mines on your way, and then head to Wickes, Montana, to see the old Beehive Kilns, which will probably be gone in a decade due to degradation. You dig through your trunk, and bust out your map. It's an older one from 2007, and this is what you see.
Alright, so you'll head south on I-15 until you get to Clancy. From there you'll head south a few more miles to Alhambra, and then you'll take a road southwest until you get to Corbin. There is only one problem: This would be impossible. There is no road heading southwest out of Alhambra. Also, Corbin is in the wrong place! So, we have an imaginary road leading to a very real community which happens to be located in an imaginary place. Damn. But wait, as your wife is berating you for being lost and cartographically clueless, your downcast eyes notice another map on the floorboard under a McDonald's sack. You pick it up and behold, a Montana Department of Transportation 2011 map. You open it up, and things don't make sense.
No longer is there a road that goes south of Clancy to Alhambra. No longer does a road even exit Alhambra to the southwest. No longer is Corbin up in the hills near the National Forest Boundary. Somehow it has migrated ten miles southeast, and is on a completely different road. Now you'll leave Helena and head to Jefferson City, take the road southwest out of that town, visit Corbin, and continue down the road to Wickes. On your way home you better stop in at Tings in Jefferson City for a beer.
Is this an egregious error? I'm aware that not alot of people travel to Corbin to sight see, and even less live in Corbin (Maybe 50). But an incorrect road from an incorrect source to a real community in an incorrect location from the folks who keep track of the roads is unexpected. This is just one error, I have found a few similar ones, from MDT maps, to Google Maps, to Bing, to USGS Quads.
Cartography is not dead. The world is not mapped. For one, the world is always changing, Geography is not static. Secondly, the data is always improving. Maps are made by fallible human beings. Notice the elevation changes between the two maps. Between 2007 and 2011, the city of Townsend rose 35 feet, Jack Mountain shrunk by 13 feet, and someone kicked a rock off of Crow Peak, thereby reducing its elevation one foot. Not really. New Geodetic Controls taking advantage of more accurate Geoid estimates with more accurate instruments were probably used. I don't really know. I guarantee those numbers will change in the future as well. Maps are amazing tools. The information provided in the State Map would take Thousands upon Thousands of pages to portray that same information in text. Love your maps, but don't forget about the most useful one you have: the one in your head.