Processing NLCD for USA using Raster Calculator and tools in QGIS

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Step By Step Procedure for Processing NLCD for the USA using the Raster Calculator, Up sampling and GRASS r.neighbors NOTE: This "raster calculator" process or method is considered suboptimal to the Python script method below. The Python script method below has newer smoothing processes. However, this method does contain useful knowledge on how to use the raster calculator. It needs to be updated to match the Python script method.


We will use a predetermined file naming convention throughout this procedure for simplicity. You can use a naming convention of your choice. The below python script produces more refined scenery than this method. I left this documentation though as it is a good starting point and has examples of how you can manipulate rasters using the calculator. It was the first steps I took to learn how all this stuff works. It could be updated to match all the steps used in the python script method.


Obtain your NLCD_2019_Land_Cover from source of choice, https://www.mrlc.gov/viewer/

NLCD_2019_Land_Cover data = NLCD_2019_Land_Cover_California-Southern.tiff


Obtain your NLCD_2016_Tree_Canopy from source of choice, https://www.mrlc.gov/viewer/

NLCD_2016_Tree_Canopy data = NLCD_2016_Tree_Canopy_California-Southern.tiff


Make Deciduous Layer 255 to 0 EPSG:5070 - NAD83 - Raster Calculator

("NLCD_2016_Tree_Canopy_California-Southern@1" = 255) * 0 + ("NLCD_2016_Tree_Canopy_California-Southern@1" != 255) * "NLCD_2016_Tree_Canopy_California-Southern@1"

Output CRS = EPSG:5070 - NAD83

Output Layer = California-Southern_deciduous-coast-clipped.tiff

OK


Make Tree Canopy Layer EPSG:5070 - NAD83 - Raster Calculator

Use the prevailing tree type, for Deciduous use * 41, for Evergreen use * 42, for MixedForest use 43.

Later we add this Tree Canopy layer to the raster where there is currently no trees in the NLCD

If ocean bordering with index 255 -

("California-Southern_deciduous-coast-clipped@1" != 0) * 42

Else

("NLCD_2016_Tree_Canopy_California-Southern@1" != 0) * 42

Output CRS = EPSG:5070 - NAD83

Output Layer = California-Southern_deciduous.tiff

OK


Make Clipped Ocean Frontage EPSG:5070 - NAD83 - GIMP

Source = NLCD_2019_Land_Cover_California-Southern.tiff

Flood fill index 11 (blue) with 0 (black)

Export tiff = California-Southern_coast-clipped.tiff


Warp NLCD Deciduous and Base NLCD from EPSG:5070 - NAD83 / Conus Albers NLCD to Project CRS: EPSG:4326 - WGS 84 - WARP

If ocean bordering with index 255

Warp California-Southern_coast-clipped.tiff

Else

Warp NLCD_2016_Tree_Canopy_California-Southern.tiff

and

Warp Deciduous NLCD from EPSG:5070 - NAD83 / Conus Albers NLCD to Project CRS: EPSG:4326 - WGS 84

Warp California-Southern_deciduous.tiff

Raster -> Projection - > Warp

Target CRS = EPSG:4326 - WGS 84

Resampling method to use = Nearest Neighbour

Output data type = byte

Reprojected = California-Southern_4326-84.tiff and California-Southern_deciduous_4326-84.tiff

Run


Combine "California-Southern_deciduous_4326-84.@1" and "California-Southern_4326-84@1" - Raster Calculator

This step adds the Tree Canopy layer to the existing NLCD raster only where there is currently no existing tree land cover.

(("California-Southern_4326-84@1" > 0 AND "California-Southern_4326-84@1" != 41 AND "California-Southern_4326-84@1" != 42 AND "California-Southern_4326-84@1" != 43) AND "California-Southern_deciduous_4326-84@1" > 0) * "California-Southern_deciduous_4326-84@1" + ("California-Southern_4326-84@1" = 41 OR "California-Southern_4326-84@1" = 42 OR "California-Southern_4326-84@1" = 43 OR "California-Southern_deciduous_4326-84@1" <= 0) * "California-Southern_4326-84@1"

Output CRS = EPSG:4326 - WGS 84

Output Layer = California-Southern_adjusted.tiff

OK


Re-class urban 21, 22, 23, 24 = grass 26 - Raster Calculator

This step is being used to erase all the man made clutter on the raster with grassland. Instead of grassland you can replace it with any type of prevailing groundcover in the area your processing.

For example this places a road easement of grass on all the road clutter that was originally in the raster. If your processing a desert area you might want to use dirt or sand instead of grassland. For Arctic areas maybe use tundra.

Part of the clutter gets replaced later in the process.

("California-Southern_adjusted@1" = 11) * 41 + ("California-Southern_adjusted@1" = 12) * 34 + ("California-Southern_adjusted@1" = 21) * 26 + ("California-Southern_adjusted@1" = 22) * 26 + ("California-Southern_adjusted@1" = 23) * 26 + ("California-Southern_adjusted@1" = 24) * 26 + ("California-Southern_adjusted@1" = 31) * 27 + ("California-Southern_adjusted@1" = 41) * 26 + ("California-Southern_adjusted@1" = 42) * 24 + ("California-Southern_adjusted@1" = 43) * 25 + ("California-Southern_adjusted@1" = 51) * 30 + ("California-Southern_adjusted@1" = 52) * 29 + ("California-Southern_adjusted@1" = 71) * 26 + ("California-Southern_adjusted@1" = 72) * 32 + ("California-Southern_adjusted@1" = 73) * 31 + ("California-Southern_adjusted@1" = 74) * 31 + ("California-Southern_adjusted@1" = 75) * 32 + ("California-Southern_adjusted@1" = 81) * 18 + ("California-Southern_adjusted@1" = 82) * 19 + ("California-Southern_adjusted@1" = 90) * 25 + ("California-Southern_adjusted@1" = 95) * 35

Output CRS = EPSG:4326 - WGS 84

Output Layer = California-Southern_reclass-grass.tiff

OK


Make Urban layer

("California-Southern_adjusted@1" = 21) * 10 + ("California-Southern_adjusted@1" = 22) * 1 + ("California-Southern_adjusted@1" = 23) * 1 + ("California-Southern_adjusted@1" = 24) * 2

Output CRS = EPSG:4326 - WGS 84

Output Layer = California-Southern_urban.tiff

OK


Remove the road clutter with r.neighbor

GRASS/Raster/r.neighbor

Neighborhood operation = median

Neighborhood size = 7

Neighbors = California-Southern_urban-only.tiff

Run


Combine "California-Southern_reclass-urban@1" and "California-Southern_reclass-grass@1"

This step replaces the "cleaned up" urban areas back into the raster.

("California-Southern_urban-only@1" < 1) * "California-Southern_reclass-grass@1" + ("California-Southern_urban-only@1" != 0) * "California-Southern_urban-only@1"

Output CRS = EPSG:4326 - WGS 84

Output Layer = California-Southern_adjusted-combined.tiff

OK


Up sample California-Southern_adjusted-combined.tiff 2x, 4x or 8x resolution 0.00008309125

Active Layer = California-Southern_adjusted-combined.tiff

Layer/Save As

2x Horizontal = 0.00008309125

2x Vertical = 0.00008309125

4x Horizontal = 0.00010637625

4x Vertical = 0.00010637625

8x Horizontal = 0.00005318812

8x Vertical = 0.00005318812

File Name = California-Southern_final-prep-4x.tiff

OK


Simplify California-Southern_4326-84-hd.tiff with r.neighbor

GRASS/Raster/r.neighbor

Neighborhood operation = median

Neighborhood size = 7

Neighbors = California-Southern_urban-only.tiff

Run


Reclass index 0 to 44, leave the rest the same

("California-Southern_4326-84-hd@1" = 0) * 44 + ("California-Southern_4326-84-hd@1" != 0) * "California-Southern_4326-84-hd@1"

Output CRS = EPSG:4326 - WGS 84

Output Layer = California-Southern_4326-84-hd-corrected.tiff

OK


Optional HD Fresh Water Option

Step 1 - Obtain and load hi resolution vector layer Make sure that the vector layer and the raster layer you will eventually merge to have the same projection. ** Extent can be different if you use the option below.

Use Top Menu: "Raster" -> "Conversion" -> "Rasterize (vector to raster)" or Processing Toolbox: GDAL -> "Vector conversion" -> "Rasterize (vector to raster)" Input layer = Southern-California_water_4326-84 Fixed value to burn = 41 (water) Output raster size units = "Georeferenced units" Width/Horizontal resolution = 0.00008309125 (4x the base NLCD resolution ) Height/Vertical resolution = 0.00008309125 (4x the base NLCD resolution)

    • Output extent = Select the raster layer you will eventually merge with as the "Output extent".

Under "Rasterized" choose a new filename to save the new raster to. We'll use Southern-California_4326-84-hd-water.tiff. 

  Click "Run" to generate the hi resolution raster layer.

Step 2 - Reclass hi res, smoothed water to grass Open Raster Calculator Under "Output layer" choose a new filename to save the new raster to. We'll use Southern-California_4326-84-hd-nowater.tiff. Copy the following into the "Raster Calculator Expression" box. Where Southern-California_4326-84-hd is the name of your hi resolution, smoothed NLCD that includes the water data. "Southern-California_4326-84-hd@1" * ("Southern-California_4326-84-hd@1" != 41) + 26 * ("Southern-California_4326-84-hd@1 = 41") 

  Click on "OK". When finished you will have a new raster with the water layer changed to grassland. Another choice would be to change it to sand.

Step 3 - Combine the hi resolution no water raster and the hi resolution water raster. Use Top Menu: "Raster" -> "Miscellaneous" -> "Merge" or Processing Toolbax: GDAL -> Raster Miscellaneous -> Merge Input layers = Select "Southern-California_4326-84-hd-nowater@1" and Southern-California_4326-84-hd-water.tiff Output data type = "byte". Under "Merged" choose a new filename to save the new raster to. We'll use Southern-California_4326-84-hdwater.tiff. 

  Click "Run" to generate the new merged hi resolution raster layer.
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