Most of the info on any gps program comes from maps or maps that are overlayed on the photo's. There isn't someone setting on a computer all day marking stuff on the photo or info being reported by hunters or anyone. I'm sure that some company's do some accuracy checking.
Most of the accuracy has to do with the map and its age. If there is nothing of value in an area then the Forest Service, BLM or USGS are slow to update maps because there is no money in it and a 1960's map is good enough. In areas where there is money to be made or a lot of land activity then maps are kept up to date. You see a lot of old maps in the sage or pinyon juniper forests were there isn't a lot of timber or land value and nothing is really changing out there unless its in an area where there drill for oil and gas then updated maps are coming out every few years.
Same can be said with Ariel photo's, ever wonder why the quality of a photo drops out in the middle of no where sage brush city? The photo is probably from the 1960's and something around 1:40000 scale while a good photo of timbered land is at 1:16000 or 1:24000 scale. Photo's do seem to be improving overall the last few years which is probably due to our current technology and multiple company's offering map services.
So the accuracy of anything on a map or photo is only as good as the data that was entered and the only way to know for sure if something is there is a little photo recon and in the end ground truthing. The spring that was added to the map in the 1960's could be long since dried up.
