Does anybody know what those white crosses painted in parking lots are for? They’re perhaps 3’ long and across, and sometimes there’s something similar to a metal cap in the middle of them where the perpendicular lines meet.
Thanks!
Without seeing an example of what you’re talking about, my guess is some sort of utility marking. Utility companies mark the paths of pipes and cables and the position of access covers for either thier own use when doing maintenance, service extensions or upgrades or for the benefit of other utilities and contractors so they know where to dig (or, rather, where not to dig).
I work for a Utility company, and those markings are usually done with spray paint and are temporary. The crosses of which I speak appear to get painted when the lines marking parking spaces are done, though they appear in the roadways or other open spaces; in other words, I’ve never seen them painted inside or across parking spaces.
if they have the metal cap, those are survey markers. The 3’ cross is painted so the survey makers can be seen on aerial photographs. It helps the city or county to construct their maps.
Sounds like marking of utilities or survey reference points, as mentioned upthread.
To elaborate, when aerial photography is done, various things like manholes and survey markers are marked. These locations are also surveyed. When the aerials are ortho-referenced, these white X’s are aligned with the surveyed coordinates in the GIS system to make the photograph match the real world.
Do you have a photo of what you’re describing? I can’t think of any traffic marking like it. Are these crosses painted with the same striping paint that the parking lot is? What part of the world is this in?
As a matter of fact, I do have a photo, but I don’t know how to upload it to the thread… any help would be appreciated there.
I live in Las Vegas, NV, though I’ve seen these crosses in other parts of the US, including CA and OR. And they’re not limited to parking lots, though I tend to see them most often there. I’ve seen them in streets occasionally as well.
The survey reference points for aerial photography would make sense.
You can’t upload a photo to the thread directly, but you can use websites like Flicker, and link to the photo.
Those are used in my line of work: Aerial Photography & Mapping.
The metal caps are surveyor’s benchmarks, the huge white crosses are visible from the air in photos.
Maps are made from the photos.
>I’ve seen these crosses in other parts of the US
Ditto the others re aerial photography and surveying. But, a test - are the crosses you are seeing visible from above? Because if you are describing things that are under heavy cover, it’s possible we are missing something here.
BTW, Hi, Bosda, I’ve gotten nice aerials here and there since we corresponded here on the subject, thanks!
djgrendellv mentioned (post #3) that these were painted at the same time as the parking lot was striped, and weren’t the same as temporary markings. That puzzles me.
Surveyor’s benchmarks aren’t temporary; they can be used for years.
I didn’t mean the benchmarks were temporary, I meant the paint. See post #3 (“markings are usually done with spray paint and are temporary”).
Although, I have been looking for benchmarks before and not found them. “Cotton picker spindle in a 10” oak tree, 14 feet north east of the intersection of Third and Washington Streets". Oops, there is a mall there now - no more benchmark! 
That reminds me of another question though, Bosda: I’ve noticed a lot more use of some type of plastic sheeting-type stuff for the ‘X’ (aerial photography reference mark). Is that a new trend in aerial mapping?
The painted marks used to locate spots in aerial photographs aren’t temporary. Spraypaint for utilities is temporary; that was the point of post #3 I think. The aerial photo reference marks look like parking lot stripes (though my impression is they’re usually a little wider).
I think they would not be in parking spaces per se, because cars would often hide them. They can’t stop the plane to move them because they are on a tight schedule, or something.
Interestingly there is what I am certain must be an aerial reference mark on the road in front of the neighbor’s house, under fairly heavy deciduous tree cover. I have puzzled over this and decided that it must be visible from the air often enough, or perhaps from some particular angle, so as to be worthwhile. There isn’t anyplace else within sight of this spot where they could have painted one with good visibility. And, there is an intersection very close to the spot, and mapping programs often show this intersection pretty inaccurately, I suspect because it’s so hard to see from above.
Try the above link for the photographs.
You’ll notice that one side of the cross has been rubbed out, and there’s also a bit of asphalt having been removed from the center. I don’t know if you can see it in either picture, but there’s what appears to be a metal spike coming out of that missing asphalt, which I suppose once held the metal cap I’ve seen associated with these. The paint is definitely not temporary, as it’s the same color as the parking space lines.
Huh. Often here, they fade with time and aren’t repainted. Of course, that might be a function of the weather and the paint, not the intent - and of the low frequency of aerial photos being taken.
Aerial photos taken for engineering purposes are done in the wintertime (often February here), so that the deciduous trees are bare. Perhaps as you say this was the best spot even though it was under tree cover, since the photos can be taken in winter.
djgrendellv: That looks just like the aerial photo crosses. Could be that the ‘metal spike’ is a pin or PK nail and never had an actual cap on it. Or as you say it may have been displaced.
Thanks everybody for the help!
>Huh. Often here, they fade with time […]
Huh again. The whole road fades with time. Some years ago there was in these parts a large government operation with loads of barracks, streets, administrative buildings, and so forth. 25 years ago I drove around this ghost town for some time, looking at the abandoned and vandal gutted buildings. Well, last week I got the chance to do it again, on a tour, and many of the roads are now hard to follow, their paving substantially swallowed by nature. Oddly, though, there are patches here and there that as far as I could tell might be new. In fact, I’d like to think the same is true of me, too.
I think it’s just to make it easier to remove the mark later. Some land owners don’t like big white crosses on their property.
I have a follow up question, now that I know what the purpose of these white crosses are. Is there some specified layout on how these are arranged? In other words, are they placed, say, 5000’ away from each other? Or are they placed wherever there just happens to an unobstructed view for planes to take pictures?
I am far from an expert, but here’s what I know:
From the ground, you won’t notice any pattern to the arrangement, but there are rules that determine it.
The crosses are placed so that they appear in the aerial photographs according to a bunch of very complicated specifications that affect the accuracy of the map.
For example, the mapmakers have to account for distortion in the photo,so the crosses are scattered , some in the center of the photo, and some close to the corners of the photo’s negative.
The exact physical locations are determined by the ground conditions. You need an unobstructed view from the air, and you need permission from the owner of the land , you need a place to physcially set up a survey instrument without it getting run over by traffic (or stolen*). And often you need a clear line of vision between each location.
So first you decide approximately where you need the crosses to appear in the photo, and then you go out in the field and improvise. 
(*don’t ask me how I know this… )
(also, it is highly recommended that the guy in the airplane does not spill a cup of coffee on the camera after takeoff )