Sampling
A grid composed of 1 9 1 km cells was overlaid on an image
of Northeast Thailand for the area from 14000N–100500E to
18300N–105400E. This grid covers all of Northeast Thailand
with a total of 176,669 grid cells (there are 501 cells on the
north–south axis and 521 cells on the east–west axis). Initially,
350 of these grid cells were randomly selected but, after
checking the Point Asia images, 147 cells had to be excluded
from the survey because they were found to be unsuitable for
analysis. Of these, 88 grid cells had no satellite images or the
images could not be utilized because of too much cloud cover
(25.1 % of the initial sample of grid cells); 59 grid cells
(16.9 % of the initial sample) had satellite images but contained either no paddy fields or such a small area of paddy
fields as to be unusable. The images for the 203 remaining grid