The .stx file contains the statistics of the .bil format file, while the *.blw file contains information on the spatial resolution.
The .stx file reads (from left to right):
band minimum maximum mean standard deviation
Unfortunately, the mean and standard deviation are distorted by the inclusion of no data values as zeroes in their calculation. The ‘band’ is present for satellite data, which can have multiple bands of information in the same bil file, and is not applicable to the GPW file (it is always 1).
The .blw file reads (from top to bottom):
dimension of one pixel/cell in the x-direction
rotation term (always zero for GPW data)
rotation term (again, always zero for GPW data)
negative of the dimension of one pixel/cell in the y-direction
x coordinate of the center of the upper-left pixel/cell
y coordinate of the center of the upper-left pixel/cell
The grids are stored in latitude longitude coordinates; the units are decimal degrees.