how NOT to zoom, and offset on older maps
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Kimberly E. on Mar 29 2016 12:47AM #1
Maybe I'm missing something, but it seems most of the maps from before 1950ish (or a little older in some areas) are offset either west or east by hat looks to be at least a few hundred yards. I could see this making sense if it applied to all images and maps before the age of accurate GPS for the general public, but all the mid 50s and later material is fine. Is there a way to fix this, a setting I haven't found?

Also, I'm using a touchscreen most of the time; how does one move north or south without zooming? There's got to be a way of turning that off. I'm guessing it works normally with a mouse. Someone please tell me what I'm missing :)

Otherwise, awesome service you're providing!
Jeff T. on Mar 29 2016 2:30PM #2
Kimberly, Can you give me an example of the area you are having issues with imagery being "a few hundred yards" offset? That would have to be a mistake or something that was missed in our QC process. Or we have a glitch that I'm unaware of. Address, coordinates, or zip code, anything would help.

As far as the panning around without zooming with a touchscreen. That's something that we haven't really addressed or been made aware of being an issue. I believe most people use a mouse. However, I pulled out my laptop to test this and understand what you're experiencing. For now, I would say if you want to pan around move to the left or the right first before you drag up or down. Essentially you have to drag left or right to get the screen moving then you can go north or south. Otherwise you'll zoom in our out. I'll talk with the programmers and see if this is something we can look into a solution for.

Kimberly E. on Mar 29 2016 11:45PM #3
I heart my touchscreen but it's not a major issue, just annoying. Oddly it works fine on my phone, can drag any direction and only zoom when it's wanted; it's just on the laptop that it happens.

As far as the offset, a good local example is Deer Park WA. Check where Dalton Rd (same thing as Old Colville Rd, more common on older maps.) Current images and any maps back to the 1951 edition will exactly match the overlay and definitely correct. If you switch to 1939 or earlier, the same road is off to the right. This happens on every overlay/map combo I've tried anywhere in the country where I'm familiar with the streets, on any maps before the 40s and in some areas as late as the mid 50s. Anything after 1960 seems to match fine every time. Is there a setting I need to change?
Jeff T. on Mar 30 2016 10:42AM #4
It looks to me like you're referring to the Topographic maps? The buttons with a "T" before the year? I see what you're talking about if that's the case. Much of this data was compiled in bulk and as far as I know it was fine previously. We did move these Topos from one server to another a couple months back. I'm going to check with our programmers and see if something may have been missed in the copy, if something was corrupted prior to a certain date, or if the data was always this way and we just didn't notice. Thanks for following up and letting us know. I was worried you meant the aerial photos, I thought maybe a batch of images got put up in an incorrect projection and ended up out of place. Looks like this could be something else. I'll look into it.

Kimberly E. on Apr 4 2016 9:16AM #5
Exactly, it's just the maps. Aerials are fine including the older ones (love how many 50s turn up!)
Donald M. on Jun 27 2016 6:53AM #6
If Historic Aerials is using the georeferencing for vintage (pre 1947) topo maps as provided by the USGS, they will be off by around 500m laterally. I found this out by exporting historic topos from the USGS TopoView site in kmz format and then importing them into Google Earth.

This only happens with maps older than the 7.5' quadrangle series which started production in 1947. This series is accurate, but the older 15' and 30' series are all off. I thought the issue might regard different datums, if the problem series used NAD27 and the newer series NAD83. However, I used a coordinate transformation program and found out that the difference in my location of interest (the Black Hills of South Dakota) amounted to less than 70m. That's no where near the 500m displacement on the USGS maps.

I posted this issue on the Google Maps forum to see if any of the mapping experts there could explain what was going on, but it was not resolved.
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