I'm calculating the average land gradient (in degrees) in Brazil and I do not know how to interpret the results.
As I'm calculating the slope in degrees, 0.25 is 0.25 degrees, 25 degrees or should I use a conversion factor?
If I construct a raster with rows of height from 1 to 10, in a square 10x10 grid of cells of size 1m, I've created a 45 degree slope:
> r = raster(matrix(1:10,10,10), xmn=0, xmx=10, ymn=0, ymx=10)
I have to give it a geometric coordinate system - so this is now a 10x10 metre area near the origin of the UK metre grid system:
> projection(r) = CRS("+init=epsg:27700")
and its slope is:
> terrain(r, unit="degrees") class : RasterLayer dimensions : 10, 10, 100 (nrow, ncol, ncell) resolution : 1, 1 (x, y) extent : 0, 10, 0, 10 (xmin, xmax, ymin, ymax) coord. ref. : +init=epsg:27700 +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +datum=OSGB36 +units=m +no_defs +ellps=airy +towgs84=446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894 data source : in memory names : slope values : 45, 45 (min, max)
45 degrees everywhere. So your 0.25 is 0.25 degrees, which is quite near level.