Why are some USGS Topo buildings black vs purple?

0	Edit link with layer USGS Topological Map has some buildings in black while others are purple. Why? colors legend usgs asked 03 Dec '14, 19:09 cwholemanii 16●1●1●3 accept rate: 0%

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On the older USGS topo maps for my area the legend at the bottom indicates that the purple are map revisions. So the black are the buildings that were there when the map was first issued, and the purple are additions when the map was reissued with revisions.

For my area I have old printed USGS maps and could give you dates for issue and revisions, but I don't know if I could find them on the web for your area. You might try the national map site to see if they are available and then look at the legend area. http://nationalmap.gov/viewer.html

Edit: Just noticed you are in California. You can also get scanned USGS maps at http://libremap.org/data/state/california/drg/

Edit again: Your Julian quadrangle was issued in 1960 (black buildings) and "revisions shown in purple and woodland compiled from aerial photographs taken 1985 and other source data. Partial check by U.S. Forest Service. Map edited 1988"

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answered 03 Dec '14, 21:20

n76
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accept rate: 17%

edited 03 Dec '14, 21:29

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question asked: 03 Dec '14, 19:09

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last updated: 03 Dec '14, 21:29

Why are some USGS Topo buildings black vs purple?

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