>GIS data can be 3D by the way. E.g. geojson uses an array for coordinates and the third position is reserved for altitude. It's just that a lot of GIS data set

>GIS data can be 3D by the way. E.g. geojson uses an array for coordinates and the third position is reserved for altitude. It's just that a lot of GIS data sets don't include altitude information. yes, its why I said relative positions and elevations. >One interesting aspect of GIS data is that coordinates are not exact. They can be off by meters and misaligned with other data sets. It often depends on relative projection etc. The coordinates are exact, but if you're getting them from a source with a relatively high inaccuracy they may just be wrong, or disagree with another data source. As I said, when it really matters a survey crew goes out and does things to a much higher degree of accuracy than 'a few meters', or a lidar scan takes very accurate measurements that are accurate to mm not meters. The case in the article where they're looking at a construction site and making decisions based on the information would get a digital file from the survey crew based on a nearby survey benchmark, not from GPS. When using actual surveying tech based on GPS the accuracy is much higher than 'GPS', and errors in properly done surveys are something like 3 cm in 30km. The issue is that people are using data not intended to make detailed plans, to make detailed plans, because they don't want to pay for surveying. When surveying is paid for, the map is accurate to millimeters not centimeters or meters as you say. Tectonic plates shifting are unlikely to be a measurable issue in the overwhelming majority of projects unless you have very very long term projects that are very large, in which case the thermal expansion of materials is likely to make a much larger variability than any plate movement.