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 contagion map portrays relative contagion, at one scale, considering only the MRLC land cover types.
Land cover data (MRLC) was obtained from EROS Data Center in binary format.
The bsq 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 classes appear in the MRLC map. 11: open water (missing) 12: perennial ice/snow (missing) 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 27x27 pixel quadrat was centered on each pixel of the original land cover map. An attribute adjacency table was then tabulated, considering only pixel pairs in cardinal directions (i.e., four neighbors per pixel), and counting each pixel pair once. The contagion index was then computed from the attribute adjacency table by first dividing each cell in the table by the total number of pixel pairs, then summing the main diagonal elements. This yields a value of 0 when, for all land cover types, there are no pairs of adjacent pixels which have the same cover type. The maximum value of 1 is obtained when all pixels are adjacent in all cardinal directions to other pixels of the same type. Thus, the range is from zero (low contagion) to one (high contagion).
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 27x27 pixel window 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.