I am attempting to download and use your 1990 Adjusted Population Numbers for Africa. I have successfully downloaded the zipped BIL file. In order to convert this for use in my GIS software (I am using IDRISI) I need to know information which I cannot find in any of the documentation files you have made accessible. Please can you answer the following questions regarding the BIL format: 1. Is there a header - if so what is its size? 2. What are the maximum and minimum grid co-ordinates for your Africa data? 3. Are the data 8-bit or 16-bit? 4. What reference system do you use, and what the reference units measured in?

1. The actual data file (afp90agi.bil) has no header itself, instead the information is contained in a separate file (afp90agi.hdr) that should come bundled in the zip file.

2. The bounds of the data file are:
xmin -30.0
xmax 60.0
ymin -40.0
ymax 40.0

3. The data are actually 32 bit.

4. The reference system is geographic (not projected), the units are decimal degrees and the spheroid is World Geodetic System, 1984 (WGS84).

Please note that the byte order is Motorola (UNIX), not Intel. I believe that Idrisi has a command that will change the byte order to Intel. If I recall correctly, the command in Idrisi is called ‘flip’.

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