NLCD Land Cover

NLCD2016 land cover example, south shore of Long Island, NY

About

• Raster grid covering the Continental US at 30 meter resolution

• https://www.mrlc.gov/data/nlcd-2016-land-cover-conus

From the Spearfish dataset's landcover.30m history file:

National Land Cover Data Set NLCD, U.S. Geological Survey (USGS)

The NLCD was compiled from Landsat TM imagery (circa 1992) with a spatial resolution of 30 meters supplemented by various ancillary data (where available). The satellite images were analyzed and interpreted by using very large, sometimes multi-State, image mosaics (that is, up to 18 Landsat scenes). Because a relatively small number of aerial photographs were necessarily conducted from a broad spatial perspective. Furthermore, the accuracy assessments correspond to Federal Regions, which are groupings of contiguous States. Thus, the reliability of the data is greatest at the State or multi-State level. The statistical accuracy of the data is known only for the region.

Obtaining data from the USGS

The classic Spearfish GRASS sample dataset contains a landcover.30m raster map which is an excerpt from an older version of the NLCD dataset.

• Download site: https://www.mrlc.gov/data

• Data is provided in ERDAS Imagine .img format.

As of April 2019 the zipped dataset is a 1.4 GB.

• Create an Albers location

this can also be done automatically with the Location Wizard using the downloaded .img file.

Here are the values for the CONUS dataset:

name: Albers Equal Area
proj: aea
datum: wgs84
ellps: wgs84
lat_1: 29.5
lat_2: 45.5
lat_0: 23
lon_0: -96
x_0: 0
y_0: 0
towgs84: 0,0,0,0,0,0,0
no_defs: defined

Importing

Rather than import the entire 16GB raster image, just make a virtual link to it:

r.external in=NLCD_2016_Land_Cover_L48_20190424.img out=NLCD_2016_Land_Cover_L48_20190424 title="Land Cover 2016"

Then use g.region to zoom to your area of interest and r.mapcalc to extract a subset

g.region -p n= s= e= w= res=30 align=NLCD_2016_Land_Cover_L48_20190424
r.mapcalc "NLCD.extract = NLCD_2016_Land_Cover_L48_20190424"

Categories

These can be applied with the r.category module.

0:Unclassified
11:Open Water
12:Perennial Snow/Ice
21:Developed, Open Space
22:Developed, Low Intensity
23:Developed, Medium Intensity
24:Developed, High Intensity
31:Barren Land
41:Deciduous Forest
42:Evergreen Forest
43:Mixed Forest
52:Shrub/Scrub
71:Herbaceous
81:Hay/Pasture
82:Cultivated Crops
90:Woody Wetlands
95:Emergent Herbaceous Wetlands

Colors

NLCD2016 land cover classification legend from mrlc.gov

These should load in automatically, but if they don't here are the official colors which you can load in with the r.colors module's rules= option:

11 70:107:159
12 209:222:248
21 222:197:197
22 217:146:130
23 235:0:0
24 171:0:0
31 179:172:159
41 104:171:95
42 28:95:44
43 181:197:143
52 204:184:121
71 223:223:194
81 220:217:57
82 171:108:40
90 184:217:235
95 108:159:184

Legend

Use the -n and -c flags of d.legend to limit the legend to named categories.

• See also https://www.mrlc.gov/data/legends/national-land-cover-database-2016-nlcd2016-legend

Manning's n

For using as a basis for Manning's n friction coefficients, you can make a virtual reclass map with r.reclass. The module will only reclass as integers so the table below is reclassed into parts per thousand. Crop your area of interest with r.mapcalc and divide by 1000.0 at the same time to get the Manning's n number.

Actual values for your location will vary widely, the following is simply a starting point.