Caveats include: Maps in this series are naturally correlated since all came from one map. No warranty or claim is made of the utility of this map for any particular purpose, this is considered to be a research dataset. The land cover diversity map portrays relative diversity, of cover types recognized by the MRLC, using a selected diversity index at one spatial scale.
The objective is to estimate Simpson's (1949) diversity index by using the proportions of land cover within fixed-area analysis windows, and to map the resulting index value.
Land cover data (MRLC) was obtained from EROS Data Center in binary format.
The image was subdivided into sixteen (16) overlapping rectangles using an in-house software tool named SPLITTER.C. The rectangles overlapped to avoid artifacts near image boundaries during the spatial filtering operations.
Each of the rectangles was then processed via spatial filtering to estimate the index as described below. The spatial filtering program is an in-house software tool named SPATCONV.C (Riitters et al. 1997)
After spatial filtering, a map of index values was constructed by reassembling the 16 rectangles into a single image (via an in-house software tool named LUMPER.C, which removed the overlapping parts of rectangles).
The "header file" information for the derived map is as follows. This information is needed for some image import filters. Ulxmap and Ulymap refer to the center of the upper-left pixel. nrows 13240 ncols 13265 nbands 1 nbits 8 layout bsq skipbytes 0 ulxmap 1154670.000000 ulymap 2064600.000000 xdim 30.000000 ydim 30.000000
Spatial filtering proceeded as follows.
The following land cover types are recognized by the MRLC land cover map.
11: open water 12: perennial ice/snow 21: low intensity developed 22: high intensity residential 23: high intensity commercial/industrial 31: bare rock/sand/clay 32: quarries/strip mines/gravel pits 33: transitional barren 41: deciduous forest 42: evergreen forest 43: mixed forest 51: deciduous shrubland 52: evergreen shrubland 53: mixed shrubland 61: planted/cultivated (orchards, vineyards, groves) 71: grassland/herbaceous 81: hay/pasture 82: row crops 83: small grains 84: bare soil 85: other grass (lawns, city parks, golf courses) 91: woody wetland 92: emergent herbaceous wetland
A 65.61 ha (27x27 pixel) quadrat was centered on each pixel of the original land cover map. The numbers of pixels in each cover type were tabulated for the non-missing pixels in the window. The index was then computed as one minus the sum of squares of land cover proportions within the quadrat. The index ranges from zero to one, with larger index values taken to represent more land cover diversity.
If the center pixel was "missing" in the land cover map, then the index was assigned a "missing" value. Note that the index is defined for all other land cover types.
The calculated values were discretized to the range [1,255] and stored at 30-meter spatial resolution. Thus, a pixel value in the new map represents the index for the surrounding 65.61 ha in the original land cover map.
The transformation used to discretize the values was: D = ( C * 254 ) + 1 where D = discretized value in range [1,255] C = calculated value in range [0,1] If needed, the original calculated values can be approximated by applying the backtransformation: C = ( D - 1 ) / 254 The backtransformed values will be in steps of size approximately 0.00394 as a result of the discretization process.