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Home - General / All posts - Using the USGS GAP/LANDFIRE National Terrestrial Ecosystems 2011 tiffs

386 post(s)
#30-Aug-19 22:47

I downloaded and imported the geotiff and it worked right the first try (yeah I know a miracle since they have a 7 line tfw file). Each pixel represents a cover 30x30 m cover type and is color coded by the type (I haven't figured out what exactly that means yet). There is a an accompanying spreadsheet with RGB values for each cover type. What I would like to do is somehow transfer this information to a watershed polygon and get a count of pixels by RGB values, then I can handle the rest. What I plan to do with it is get land cover type % for each polygon. I can't find a way to do that in the help file.


386 post(s)
#30-Aug-19 23:07

Whoops forgot to say that it shows up in black and white. The old tiff (2005 I believe) was in color. I can deal with the old file too (I'm not that picky) but the same goes for it.

9,111 post(s)
#31-Aug-19 04:51

A quick reply:

I would try (1) tracing areas from pixel values, followed by (2) a topology overlay, identity method, with watershed areas as the target drawing and the result of (1) as the overlay.

Then, to get the percentage of each landcover type for each watershed area, the simplest thing might be a pair of joins: first a cross join of original watershed areas to a simple table of class codes (landcover image values), then a left join of that result to the result of (2) above.


386 post(s)
#31-Aug-19 18:02

Thanks a bunch, sounds like Greek to me! I'm on a tight schedule so I don't have the time but for once I have a budget. I hope it's OK to ask on here but if anybody needs however long it takes of freelance work can you please contact me via my website?

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