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This is a followup question to: Determining percent land coverage around points of interest using NLCD and QGIS

I am looking to determine the percent of various landcover types (wetlands, forest, etc.) in areas of various radii surrounding a breeding location using the NLCD database. Using help I received with my previous question, I was able to generate shapefiles representing all of my desired radii. The response to my question also linked me to a video showing how to determine the various percentages of landcover in my buffer zones. However, the video showed the use of a Shapefile for the land coverage instead of the raster file. When I downloaded the NLCD database, I got files with the following extensions: .rrd, .rde, .img, .ige, .xml and a folder called spatial metadata with files named spatial_metadata with extensions of .shx, .shp, .sbx, .prj, .dbf, .cpg, .txt. When I open the .shp metadata file, it just shows the US as a solid color. When I open the .img file, I see the landcover usage that I would like.

How can I go about getting a file (or files if I need to have one for each land cover category) that I can use with the buffer zones to calculate percentage?

I have done the raster to vector (polygonize) command, but when it finishes running, it says there is an additional layer called "vectorized" however that layer is completely empty when I try to view it.

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  • when you open the .shp file in QGIS, is it all one polygon or is the US broken up into multiple polygons?
    – csk
    Sep 24 '19 at 18:59
  • What it looks like to me is that the US is covered by a bunch of squares all of the same size and color imgur.com/a/PeMYvLY and when I click on one of the squares I get something like this imgur.com/a/mpDijkd Sep 25 '19 at 20:21
  • The second image is the Identify tool information for a single polygon. It looks like they have a lot of different attribute table fields. One or more of those fields should represent a land cover type. You just need to figure out which field represents land cover type, and what the different values mean. Then you can classify the layer based on that field, and each land cover type will be a different color on the map.
    – csk
    Sep 26 '19 at 15:18
  • Hopefully the different categories are explained in one of the files that came with your download. Is there a text file called "metadata" or "readme" or anything that looks like it might have an explanation in it? What does the .xml file look like if you open it in a text editor (eg Notepad)?
    – csk
    Sep 26 '19 at 15:21
  • the fields called "2001_base_", "2004_base_", etc, look promising. All of them in your example have values that start with 'LT05_', followed by the relevant year, followed by a 3-digit value like '133'. My guess is that that final 3-digit value is the land cover class for that square for that year.
    – csk
    Sep 26 '19 at 15:23
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NLCD data can be downloaded as vector directly inside the QGIS by a plugin called Curve Number Generator. https://plugins.qgis.org/plugins/curve_number_generator/.

The plugin can be downloaded from the official repository inside QGIS. enter image description here

It will download NLCD LU as vector for any area under 100,000 acres within the contiguous United States.

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