[dwyerm]

This isn't a novel thing, as far as I can tell. A decade ago when I was working on routing of over-the-road trucking, our maps provider moved the entire United States a couple meters and it broke all our road restrictions.

The problem for us -- and likely for those in Australia now -- is that converting physical address descriptions and lat/long becomes a little more fraught. We described road restrictions as being "on the road that is found between X1,Y1 and X2,Y2." A separate layer would snap those X,Y coordinates to the road network and find the road between them. Before the move, that meant converting to "Highway 6 Southbound from milemarker 16 to milemarker 28"

But when you moved the world, X1,Y1 no longer landed on Highway 6, and instead snapped over to the frontage road. Your restriction now read as "Highway 6 Southbound, down to exit 21, around the corner to the frontage road, then down the frontage road". And your restriction that used to say "stay off this one section of road" now says "stay off the highway, the frontage road, and don't use this exit."

[beerandt]

While the problem isn't novel, that's probably not what happened with what you're describing, for a number of reasons.

Most local datums are anchored to the local geology. So in the US, if you're using nad27 or nad83, the reference system is "moving" along with the continent (nad83 = North American Datum 1983), based on some weighted benchmark vectors and a lot of math. It's one reason why different datums with defined epochs exist. Some are static, but some are actually dynamic with time (eg ITRF).

But most people don't grok any of that and just stick with defaults, or guess-and-check during map setup and go with whatever looks "close enough".

In your case, chances are the map provider switched datums with the update, from nad27 to nad83, and your software wasn't told about the change. Or it was, but your road restriction data was drawn in the old projection, and not converted / transformed to the new one.

Or, you could have had data that initially was mislabeled, recorded with GPS (wgs84) and entered using one of the many datums that's similar, but not the same. Or maybe collected using one of the many state plane coordinate systems (which people tend to like because it's more or less Cartesian- east,north) which are themselves built in top of one of the datums. You can pick the right coordinate zone, but wrong underlying datum.

If any data provider or aggregator or if your company GIS guru ever selected the wrong projection (choices often are dozens of coded options that look nearly identical), or left it blank (undefined) because they weren't sure...

A instant "shift" would happen as soon as you "corrected" the error, (or upgraded software, or any other number of situations).

This is where a good GIS guru earns their keep, because conversions between projections and datums are just math, and data can often be corrected in seconds by running it through a manual "inverse" conversion, assuming one can recognize what happened.

Back to Australia: if people used GPS coordinates (wgs84) and didn't convert to a Australian centric datum (which is the default option for most collectors), the data would "stay still" while the continent moves. Which is one of many reasons why selecting an appropriate datum/ projection is so important.

For the US: While there is some intra-datum movement between nad27 and nad83, most of the differences are do to improvements in the quality and accuracy of surveys over half a century. So the differences between the two datums tend to grow as you get further from the beginning points of the surveys.

Which means some areas, like a lot of the East coast, have minimal differences, and areas out West have larger deltas, but it varies.

A couple of meters would be better explained by a bad datum transformation than by drift, which is likely an order of magnitude smaller at even the worst locations for the US.