Hi. I have a dataframe called radSamp

which looks like this:

> head(radSamp[,c(3,4,5)])
  Latitude Longitude Value
1 39.16094  140.4883    45
2 32.84428 -117.2240    47
3 35.80605  139.3789    28
4 35.07816 -106.6123    50
5 35.83174  136.2027    35
6 34.78944  137.9496    32

This is radiation data from the area around Fukushima, Japan.
I want to partition this region into about 40x40 rectangles. I think that
if I can create a factor f consisting of these 1600 rectangles then I can
focus on what is happening in each of these rectangles by
using split(radSamp$Value, f).
The area I want to focus on is defined by the following 4 corners of a
rectangle:

~Akita
Lat    = 39 degrees,   41.4 minutes   North
Long = 137 degrees,   10.1 minutes   East


East of Akita
Lat    = 39 degrees,   41.4 minutes   North
Long = 141 degrees,   57.5 minutes   East

~Toyama
Lat    = 36 degrees,   42.2 minutes   North
Long = 137 degrees,   10.1 minutes   East

East of Toyama
Lat    = 36 degrees,   42.2 minutes   North
Long = 141 degrees,   57.5 minutes   East

Can anyone suggest how to create such a factor?

Thank you.

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