I have lived in Kiev and I have seen how GPS jamming works on the ground. As soon as russian missiles or drones approached Kiev, our air defense typically turned on the GPS jamming. I could immediately see on my phone that I'm steadily moving in a straight line directly northeast at a high speed in a very different part of the city - all while sitting on the couch in my home not very high above the ground. A few times like that.

I was curious how powerful should a jammer be to completely actively substitute GPS coordinates in a city so large.