OpenStreetMap
I need to vent for a minute.
Aligning aerial imagery terrifies me. I feel like no matter what I do, I will be off by a little bit. Whenever I come across a place where buildings are mapped and are a little bit off from the aerial imagery I’m using, I think to myself “I should probably align my imagery with those buildings,” but then I look at the primary road the buildings are right next to and realize that it is aligned with how my aerial imagery is right now. And then I see a cluster of features made 9+ years ago which is nowhere close to being aligned with my imagery and I question whether all of my contributions have been miles off of the correct location and if I’ve accidentally been vandalizing hundreds of places across Virginia without even knowing. But the worst feeling is when the same aerial imagery layer has its tiles slightly misaligned from the one right next to it, so I have to make the decision on which tile I should align all my changes with.
How can I achieve peace when it comes to aligning aerial imagery?
Discussion
Comment from Endres Pelka on 22 August 2026 at 09:19
Every contribution is based on different imagery, off by a different error. As long as we don’t have any high-precision sources for an area (e.g. government supplied building contours), we have to deal with it.
What’s important is making sure the topological order of features is maintained. For example, if a mailbox is located on the eastern side of the street, between the house 101 and the driveway to house 103, then put its node there on OpenStreetMap. But if you have precise coordinates of the mailbox (taken by GPS on site), then adjust the other surrounding features (street, houses, driveways) tu fulfill this order. It’s always an improvement.
Comment from AntiCompositeNumber on 22 August 2026 at 18:07
Everything has a tolerance, nothing is ever perfect. With some expensive GPS equipment you can get that tolerance down to a couple of centimeters, but most people aren’t using that. Often, aerial imagery (with all the problems you’ve mentioned) is more accurate than the GPS traces I get, unless I have a lot of data to average together.
In the US, unless you have high-quality public domain property data to work with, I generally recommend aligning off of the USGS 3D Elevation Program data. While the USGS doesn’t officially guarantee the horizontal accuracy of this data, it’s definitely close enough for our work. Using elevation data directly for this also eliminates error caused by different aerial imagery sources using different elevation data to create the flat imagery.
Close enough is close enough.
Comment from Aeiouau on 23 August 2026 at 07:27
in situations like this i try to remind myself of the fact that perfection does not exist, it is only an idea. In this ever changing world, which boils down to different rates of entropy, we’re all trying to make imperfect things perfect, but only getting progress, not ever reaching perfection. And that’s okay! Because it’s the journey we’re after, not the destination. Every node is progress. Every little bit counts, as you lay the base for others to build upon your work.