Survey Control Mark

So, while editing this week’s WeeklyOSM entry, I stumbled upon this OSM diary titled “GPX Reference Point Generator” (GPXRPG).This is a simple yet very cool tool for making OSM armchair mapping more serious and accurate. The main idea is that we use coordinate data from local government survey control mark plaques to help us “align” satellite imagery to its correct position. Local government survey control marks are usually surveyed and calibrated to a very high degree of precision, and their precise coordinate data can often be found on the local government’s website. At the same time, the physical marker is usually visible in satellite imagery. So, we take the high-precision coordinates from the local government website and then make sure that our current satellite imagery is properly aligned with those coordinates. In other words, we make sure that the plaque visible in the satellite imagery is positioned exactly where the official coordinate data says it should be.On the “User…